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1 Knowledge for Children Low Aim is a Crime, but not high ambition NCERT ‘Guidance in Schools’ A need for every Child Today at Kayalpatnam

CFCs damage Ozone Layer ?:

2 Guidance for Children CFCs damage Ozone Layer ? Chloroflurocarbons (CFC) used by refrigrants, coolants, cleaning agents, etc are main eaters of ozone present in atmosphere. Highly unstable, an ozone molecule readily splits when hit by ultravoilet radation. Energy of life-damaging UV rays is thus converted into harmless heat and never reaches the earth. This process generates Oxygen atom and Oxygen molecule, which in an ongoing cycle, recombine to form new ozone molecules. When CFCs go upward to stratosphere and get struck by ultra violet rays, it releases chlorine atom, which attacks an ozone molecule, pulls away one of the three oxygen and forms a chlorine monoxide molecule thus destroying the ozone molecule. Oxygen atoms from the new chlorine monoxide molecule is pulled away by free oxygen atoms freeing the chlorine atom to restart the cycle.

Dust – Appear & Reappear:

3 Guidance for Children Dust – Appear & Reappear Dust is mostly tiny fragments abraded from large things. Dust knows no borders. Dust cloth may simply stir up dust. Charged particles of dust are attracted to surfaces with the opposite charge. An antistatic spray may help by providing a very thin layer of insulation between the opposite charges.

Age of Fossils:

4 Guidance for Children Age of Fossils Atoms of same element having same atomic number but different mass number are called isotopes. Radio active isotope of carbon is 146C which has a half life period of 5730 years. Half life period of a radio active substance is defined as the time required for half of its atoms to disintegrate. The radio isotope of carbon is continuously produced in the atmosphere by the action of cosmic rays on atmospheric hydrogen. Plants and animals absorbs 146C with natural carbon 126C. In living beings, the ratio of 146C/126C is a constant when a plant or animal dies the 146C disintegrates without being replaced. Hence by determining the ratio 146C/126C in fossil the age is determined. This method is called “Carbon dating”.

Height of Mountains Measured:

5 Guidance for Children Height of Mountains Measured The method used is known as “Triangulation”. If one knows one side and two angles of any triangle (or two sides and one angle), one can find out the rest of its measurement. One side of the triangle is usually a level piece of ground between two landmarks. The third landmark is the apex of the triangle. The angle it makes with each of the first line is measured. Instrument for measuring these angle is called a transit. The transit works vertically which is called levelling as there is a spirit level at the base of the instrument that indicates when it is in level. By raising the sight to any landmark or a mountain, the same process of measuring angles can be done and the length of one side (the height) can be measured.

Lava is hot ?:

6 Guidance for Children Lava is hot ? Magma is predominantly a molten silicate saturated with gases that are dissolved in it. Due to high pressure existing in deeper part of the earth where volatile compounds are in a dissolved state. within magma, diminishing its viscosity and increasing the degree of its mobility and chemical activity. Volcanism unites all the processes connected with the outflow on the earth surface. Liquid products of volcanic eruptions are represented by lava.

Black and White Clothes:

7 Guidance for Children Black and White Clothes Black material radiates heat faster than white material, and similarly absorbs infrared heat faster. Although it is true that dark objects radiates heat more effectively than light-coloured ones, the amount of heat radiated from a body is proportional to its absolute temperate raised to the power of 4. In Summer, it would be better to wear white as the benefit of black clothes radiating heat away quickly would not outweigh the disadvantage of them absorbing infrared heat more quickly.

Rainfall – Measure ?:

8 Guidance for Children Rainfall – Measure ? A simple rain gauge which any one can use to measure rain at his place consists of a funnel (3 to 4 inches in diameter) fitted into a bottle (about 1 litre capacity) to collect the rain water and a measuring cylinder. An air-vent is to be provided to prevent accumulation of rain water in the funnel in case of heavy down pours. Rain gauge is kept on the ground without obstructions. If the area of opening of the funnel is 80cm 2 then for 1cm of rainfall the volume of water would be 80cm 2 x 1cm that is 80cm 3 . If the total volume of rain water (in cm 3 ) collected, over a specified period, is divided by 8, we get the rainfall in mm in that place over the given period.

Smell after Rain:

9 Guidance for Children Smell after Rain Smell immediately after a shower is due to certain volatile chemical compounds released by a group of soil-inhibiting bacteria called streptomycetes. Streptomycetes are abandant in dry warm soil, a million of them can be detected in a gram of soil. They release compounds such as geosmin and 2 methyl isoborneol when wetted by rain water after a long dry spell. Thus we get the odour only after the first rain of the rainy season. The smell can be felt in newly ploughed lands also.

Rainbow Formation:

10 Guidance for Children Rainbow Formation When the Sun shines after a shower, we often see an arc of beautiful colours in that part of the sky opposite to the Sun. This is due to reflection and refraction of the Sun’s rays as they fall on drops of rain. As a ray passes into a drop of rain, the water acts as a tiny prism. The ray is bent, or refracted as it enters the drop and is separated into different colours. As it strikes the inner surface of the drop it is further refracted and dispersed.

Mountain Tops are Cooler & not hot?:

11 Guidance for Children Mountain Tops are Cooler & not hot? Air is a poor absorber of sunlight. Sun heats the Earth which is a better absorber, and the Earth then heats the air close to it. Hot air rises because it is less dense than surrounding cooler air at the same pressure. As it rises, a mass of hot air expands because the ambient pressure is less. This expansion cools the air, so the temperature of a thermal bubble decreases with increasing altitude until it reaches an equilibrium. If you climb 40Km above the Earth’s surface, you would find that it gets much warmer.

Sound in Thunder:

12 Guidance for Children Sound in Thunder Warm, wet air surges upwards into the sky and cools dramatically forming thunderstorms. Some of the water inside the clouds freeze and strong air currents make the ice and water droplets bump together. This knocks tiny charged particles called electrons from the ice and so there is a build-up of electric charge. This charge is released by a stroke of lightning. The lightning heats the air around it to an incredible 30,000C. We hear lightning first and then thunder because light travels faster than sound. By counting the seconds between the lightning and thunder and dividing by three we get the distance to the storm in Kilometres.

Finger Cool Faster:

13 Guidance for Children Finger Cool Faster Our body is like a container of heat. The amount of heat per unit volume (say, every cubic centimetre) of the body is approximately the same. But the fingers and nose have a greater surface area per cubic centimetre than other parts of the body and so they cool down faster. As soon as heat is delivered to the fingers it escapes through the surface. But the rest of the body does it slower and so are a little hotter than the fingers.

Coconut Oil Freeze in Winter:

14 Guidance for Children Coconut Oil Freeze in Winter Oils are liquid fats. Fats are esters of carboxylic acids which are either saturated (do not contain double bond) or unsaturated (contain one or two double bond). These esters are derived from a single alcohol called glycerol and are glycerides. Fats with greater percentage of unsaturation tend to be in liquid state and fats with greater percentage of saturation tend to be in solid state at room temperature. Coconut oil contains nearly 91 per cent of saturated fatty acids. Still, it is liquid at room temperature because of the presence of more number of short chain (C12 and C14). Because of the greater percentage of saturation, coconut oil can be solidified at low temperature and becomes solid during winter when the temperature falls below 20 degree centigrade.

Water in Mud Pot remains cool:

15 Guidance for Children Water in Mud Pot remains cool Mud pots contain many minute pores through which water can slowly ooze out. These pores increase the surface area of water and consequently increase evaporation. For water to evaporate it requires some energy while it takes as heat from the water itself. This results in lowering the temperature of the water in the pot. Water never becomes ice because the system is not a closed system and so it can take up heat from its surroundings.

Drops are Spherical ?:

16 Guidance for Children Drops are Spherical ? Liquid drops tend to be in a state of minimum surface energy which is directly related to the surface area. The force, surface tension, which is trying to hold the droplet together, therefore tries to reduce the surface area of the drop. Mathematically only a sphere has the smallest surface area for a given volume, compared to other geometric shapes.

Sunflower facing Sun:

17 Guidance for Children Sunflower facing Sun Due to Phototropism. Phototropism is a growth-mediated response of a plant to simulation by visible light. The response is stimulated by a hormone called auxin present in the stem. Auxins promote lengthwise growth of plants.

Lotus leaf does not get wet:

18 Guidance for Children Lotus leaf does not get wet Lotus leaf does not get wet due to outlayers of cells in the epidermal layer of leaves. They contain cellulose, which get converted by cutin by the process of cutinization and form an impermeable membrane on the cell wall known as cuticule. Cuticle, is a layer of wax-like substances which are simple lipids containing one molecule of fatty acids esterified with one molecule of long chain alcohols instead of glycerol. A molecule of wax consists of odd number of carbon atoms ranging from C25 to C35. These are highly insoluble in water & chemically inert because these do not have double bonds in their hydrocarbon chains. Hence waxes from a protective covering.

Lemon drops create white spots?:

19 Guidance for Children Lemon drops create white spots? Lime juice contains 6 – 10 per cent of citric acid. Cement is a complex mixture of calcium silicates and calcium aluminates. When drops of lime juice fall on the floor, a chemical change takes place. One of the products is calcium citrate which gives a white colour on these spots.

Cut Apple turns Brown:

20 Guidance for Children Cut Apple turns Brown Apple contains an enzyme known as polyphenol oxidase (it is a copper containing enzyme). When the fruit is cut, this enzyme becomes reactive as it comes into contact with air. It reacts with the sugar present in the fruit and results in the formation of brown colour on the cut surface. If cut apple is dipped in an ascorbic acid solution browning of the cut surface can be prevented as the acid inhibits activity of the enzyme.

Temperature affect ripening bananas:

21 Guidance for Children Temperature affect ripening bananas Temperature changes can delay or hasten the ripening of banana. Banana is a tropical fruit; adapted to ripen quickly at a certain stage of its development and at a particular temperature and humidity. It continues to ripen after harvest, with more and more of its starch converted into sugars by the action of enzymes. When harvested, a banana contains about 20 percent starch and only 1 percent sugar. By the time the fruit is ripe, the proportions are reversed. Banana releases comparatively large quantities of ethylene gas to help itself ripen; the gas will even ripen other fruit put in a bag with a ripening banana.

Mango ripens in rice tin:

22 Guidance for Children Mango ripens in rice tin During ripening, a number of enzyme-assisted reactions take place inside the fruits. The list includes softening of tissues, hydrolysis, changes in pigmentation, flavour and respiration rate, and conversion of carbohydrates and organic acids into fruit sugars. These changes are induced by ethylene which is also called a ripening hormone. It has been found that during ripening, ethylene production goes up. An ethylene-forming mechanism and breaking of the insensitiveness to ethylene are attained only when fruits reach a certain physiological age. When unripe fruits are kept inside a sack or tin of rice, the time needed to attain this critical physiological age is shortened. It could be that the fruit to totally cut off from light which promotes yellowing. The ethylene produced in the fruit also diffuses rapidly through the fruit’s tissues.

Plants survive without leaves:

23 Guidance for Children Plants survive without leaves Abscission is a physiological process whereby plants shed a part, such as leaf, flower or fruit. This is promoted by a plant hormone called abscisin produced by leaves and fruits. Extreme temperatures limit the metabolic activities such as respiration, of plants. Such a reduction, consequently necessitates only a low level of photosynthetic activity. Less Energy required could be got from photosynthetic activity of a few green cells, present in the terminal regions, after all the leaves fell.

Red parts in Sugarcane:

24 Guidance for Children Red parts in Sugarcane Red portions in the stem of cane is due to a fungal disease called red-rot caused by the organism Glomerella tucumanensis. The organism attacks during the conidial stage (imperfect stage). When the affected canes are split open, the tissues of the internode which are normally white or yellow-white will become red in one or more internodes usually near the base.

Trees Reduce Air Pollution:

25 Guidance for Children Trees Reduce Air Pollution Trees act as sink for carbon dioxide. Through photosynthesis they synthesize carbohydrate using Carbon Dioxide, water and sunlight. Trees release oxygen, which is needed by other living organisms. They act as barriers or curtains for dust through the settlement on the dense foliage of trees.

Visibility in the dark:

26 Guidance for Children Visibility in the dark Vertebrates have two types of photosensitive cells, rods and cones, so called because of their shape. The rods, which are long and fat, contain large amounts of visual pigment and they mediate vision under dim illumination (scotopic vision). The cone cells, which are relatively small, mediate daylight vision (photopic vision) and colour sensation. In nocturnal animals, the retina is mainly made of rod cells. Rhodopsin, a photosensitive pigment, present in rods is decolourised by photons (light particles) and slowly regenerated in the dark. This ensures better vision for them in dim light.

Eyes glow in dark:

27 Guidance for Children Eyes glow in dark Birds’ syrinx (the functional equivalent of our larynx or voice box) is much simpler than that of humans. Some birds with more rudimentary syrinx can become more proficient in creating sound. In birds, the syrinx is located at the bottom of the trachea. Sound is produced at the syrinx as air flows and the volume is controlled by muscles in the trachea. The sounds are then emitted with little or no modulation. Human vocalisations originate from the larynx at the top of the trachea. The larynx is more complex and produces relatively simple sounds.

Eagles fly with flat wings:

28 Guidance for Children Eagles fly with flat wings Eagles adopt an energy-saving flight mode called gliding. Their broad wings and broad rounded tail enable them to exploit thermals in the air. Thermals are upward air currents in the atmosphere caused by the absorption of heat, from the sun or load, by the air. The birds flap their wings slowly and laboriously in the air in wide circles, but once they catch the rising air they begin to soar effortlessly without even a single beat up to a point where the warm air has cooled and stopped rising. From this point, they start gliding down to another thermal, which they spot by seeing other groups of rising raptors or perhaps by their delicate sensitivity to even minute changes in air currents. Their primary feathers are spread out to obtain the maximum advantage from the rising air.

Blinking Of Eyes:

29 Guidance for Children Blinking Of Eyes Blinking keeps the front of eyeball clean. Blinking is done by means of muscles in the eye lids and the cleansing by tears. The tears are secreted in a little gland and carried along to the eye and when our eyelids open and close the tears are poured over the front of eye and they wash away any particles of dust or any other harmful substances.

Run before Jumping:

30 Guidance for Children Run before Jumping Due to Newton’s law of motion: All objects living and non-living, have inertia – a tendency to remain in its present condition. If a body is at rest, it will have a tendency to remain at rest in future also. In the same way, if a body is moving, it will have a tendency to continue its movement at a later time. If we stand at a point and jump, we will not be able to cover a good distance because our body will try to remain standing (be at rest), and we will have to spend a lot of energy (or more power) to jump long distances. Thus, we run before jumping before saving.

Bees Find Their Way:

31 Guidance for Children Bees Find Their Way Information about the source of food is informed to others during round dance or waggle dance. Round dance is going in small circles, clockwise or anticlockwise, alternately. Waggle dance is tracing a figure of eight. Round dance is used if the food is of short distance [say 100m]. Waggle dance is used if the food is far away. They use round dance or waggle dance to find their way. Alternatively, they can return to the hive by remembering the angles of triangles formed by the position of the hive, the sun and bee though this may vary with time. Bees can also perceive polarisation of sunlight and thus use the sun as a compass.

Ants find their way to hidden sweets:

32 Guidance for Children Ants find their way to hidden sweets Antennae, the two hair-like structures on the head of the ants, help them in locating sweets. These chemoreceptors help them to perceive smell and taste through minute sensilla, or sensory cells. If sweets are wrapped in paper bags or any other wrappers having minute holes, the odour carried by the air will be sensed by the sensilla. If the antenna are removed, ants cannot identify the smell and distinguish them from other foods.

Ants don’t get hurt when they fall:

33 Guidance for Children Ants don’t get hurt when they fall Fall of a body is controlled by gravitational attraction of the Earth. Heavier object is attracted more than a lighter object. This attractive force is opposed by an upward thrust (resistance) offered by air on the body. This resistance also depends on the surface area of the object. That is, if the surface area is more, the resistance is also more. In the case of an ant, the force of gravity is almost balanced by air resistance and so it is able to land safely.

Ants go in a line:

34 Guidance for Children Ants go in a line Once an ant find an abundant source of food, it returns to the nest with a sample of food. While returning to the nest, it presses its abdomen to the ground and at frequent intervals extrudes its sting, the tip of which is drawn lightly over the ground surface, much like a pen drawing a thin line. As sting touches the surface, a volatile chemical (trail pheromone), flows out of a gland (Dufour’s gland), associated with the sting. In this way, the ant draws an invisible chemical line from the source of food to the nest. Since the chemical is highly volatile, the trail remains only for a short time. Hence, all ants constantly draw the line over and over again.

Houseflies increase in Summer:

35 Guidance for Children Houseflies increase in Summer A single female may lay eggs 4 to 6 times and each time each female lays 120 to 160 eggs. They lay their eggs in clusters on compost, waste heaps, manure and dumps. The condition required for laying eggs are moisture and favourable temperature. The eggs hatch in 8 to 24 hours depending on the temperature. The whitish larvae moult twice to become the familiar white maggots in 7 days. The maggots transform into quiescent reddish brown pupa from which the adult flies emerge after 5 days if the temperature is optimal. Summer provides all the favourable conditions.

Bulges when mosquito bites:

36 Guidance for Children Bulges when mosquito bites Bulging is mainly due to histamine. It is widely distributed in the tissues, the richest source being the mast cells that are normally present in the corrective tissues adjacent to the blood vessels. Preformed histamine is present in mast cell granules and is released by mast cell degranulation process which in response to the stimulus caused due to irritation at the site of the bite. This histamine causes dilation of the arterioles and increases vascular permeability venules. This in turn causes venular endothelial contraction and widening of the interendothelial cell junctions, where the extra vascular fluid accumulates causing inflammation.

Do Snakes Hear ?:

37 Guidance for Children Do Snakes Hear ? Snakes are deaf. Snakes actually respond to vibrations produced on the ground and not to the sound waves produced by the mahudi [Snake Charmer], in the air. Snakes do not have ears, instead they have a long bony road called columella auris that extends from fenestra ovalis to the quadrate bone. It is this bone which helps the snake to detect the vibrations. It is to be noted that the charmer first hit the ground with the pipe before playing it.

Spiders don’t get caught in their web:

38 Guidance for Children Spiders don’t get caught in their web Spiders secrete an oil on its legs that prevent it from sticking to their own web. Silk, made up of proteins, secreted by the silk glands, are made into fibres as thin as a thousandth of a millimetre. The proteins are water soluble when secreted, but when made into a fibre, some physical and chemical changes take place, and so, after a while the fibre becomes tough and does not dissolve in water. Spider at first makes the radials from the centre and then the spiralling threads. There may be 10-60 turns in a web. To capture an insect, spider places a small glue droplets throughout, except at the place where it rests. The vibrations of the captured insect are sensed by the spider.

Blood Clotting:

39 Guidance for Children Blood Clotting Blood has the ability to clot or coagulate, when it is withdrawn from the body. In the blood vessels, the blood remains in a fluid condition: shortly after being withdrawn, it becomes viscid and gelatinous and sets into a firm, jelly-like mass. Clot consists almost entirely of red corpuscles entangled in a network of fine fibrils or threads, composed of a substance called fibrin. It also contains platelets and plasma. Certain substances promote coagulation (procoagulants) and others inhibit coagulation (anticoagulants).

Blood Grouping:

40 Guidance for Children Blood Grouping Blood types is based on the different types of antigens present on the surface of the red blood cells (RBC). Four Groups: A, B, AB, O. The letters stand for the type of antigen present on the red blood cells. The corresponding antibodies are carried in the plasma and if the person has a particular antigen in his red cells, he can not have the corresponding antibody, since agglutination would occur. Thus group A contains antigen A and antibody anti-B. Group AB has antigens of A & B and not antibodies of either type. Group O has no antigens and antibodies anti-A and Anti-B. If the blood protein [first discovered in blood of Rhesus monkey] is present in the blood cells, then the blood cells are called Rh positive and if they are absent, it is called Rh negative.

Air we breathe out is seen in cold day:

41 Guidance for Children Air we breathe out is seen in cold day The air we exhale on a cold day is visible because of the formation of dew. The air we exhale has water vapour and carbondioxide. Our exhale air is about 40 o C but outside atmosphere is about 10 o C. Cold air cannot hold as much water vapour as warm air. Dew is formed when air is cooled to the point where it cannot hold all its water vapour, so the moisture in it begins to condense forming tiny water droplets. The temperature at which the moisture in the air begins to condense is called dew point. From 40 to 10 degree centigrade, it is cooled to below the dew point but above its freezing point. Hence the tiny water droplets float in the air and are visible.


42 Guidance for Children Myopia Myopia is defined as an eye defect where the image of the object falls before the retina of the eye. The person affected with myopia cannot see distant objects clearly, but can see objects that are close to him. Myopia is also known as short sight. Three types: Congenital Myopia: Since birth. Simple or developmental myopia: Defect increases usually as age advances. Pathological or degenerative myopia: Condition rapidly increases and there may be high myopia upto 20 D.


43 Guidance for Children Cramps Cramp can occur due to a localised muscle spasm. Pain or uneasiness is caused by nervous irritation due to accumulation of some metabolites or chemicals in that area. Massage, external compression of muscle, improves blood supply. It helps in washing away these metabolites and thus relives the cramp. However, not all cramps can be relieved by massage.


44 Guidance for Children Dandruff Dandruff is a condition of excessive scales of the scalp. There are two varieties: Dry and Greasy. Dry: The scales are fine, thin, white or greyish, and dry or slightly greasy. Lacks lusture; Mild to moderate itching; Scales will fall freely on the shoulders. Occurs more in winter than in summer. Exaggeration of normal exfoliation of the horny layer of the epidermis. Greasy: Both the scale and integument are oily. Extends to eyebrows, eyelids, beard and others. Basic defect in this case is over production and/or change in composition of the sebaceous secretion. Common at puberty and it occurs due to endocrine disorders, familial predisposition, unbalanced diet and constipation.

Antidandruff Shampoo Work:

45 Guidance for Children Antidandruff Shampoo Work Dandruff is thought to be caused by overgrowth of yeast such as Pityrosporum ovale which live on normal skin. Antidandruff shampoos work by three mechanisms: Ingredients such as coal tar are antikeratostatic and they inhibit keratinocyte cell division. Detergents in the shampoo are keratolytic: they break up accumulation of scale. Antifungal agents such as ketoconazole inhibit growth of yeast itself. Other components such as selenium sulphide also inhibit yeast growth and therefore scaling.

Cold & Flu in Winter:

46 Guidance for Children Cold & Flu in Winter Rhinivirus, which is responsible for up to 40 per cent of clods, culture better at a temperature of 32 degrees C rather than the normal body temperature of 37 degrees C. However, 32 degrees C is the normal temperature of the lining of the nose, which is good news for the virus. Children and teenagers are far more susceptible to infection as the immune system learns how to combat more infections as they get older as have been exposed to more of the 200 or so viruses responsible for the common cold. Densely packed nurseries, schools and college provide an ideal breeding ground for viruses which then spread out into the community aided by the cold damp weather.


47 Guidance for Children Hiccups Diaphragm is located between the chest and the stomach. While inhaling air this diaphragm goes down and presses the stomach due to which the lungs are filled with air. While exhaling air, the diaphragm goes up and the air comes out from the lungs. Thus the diaphragm goes up and down and the process of respiration continues incessantly without making any sound. Two sudden and involuntary contractions within the diaphragm cause hiccups. You can get hiccups if you eat too much or too fast or if you eat victuals disagreeable to your system.

Blocking Nose While Crying:

48 Guidance for Children Blocking Nose While Crying Tear fluid is secreted by a lacrimal gland seen bulging the conjunctiva (muscous membrane covering the eyeball and lining the eyelids) Tear passes through numerous ducts into the conjunctive sac, aided by ocular muscle contraction. From there it reaches the lacirne sac and through the lacrimal duct it is drained into the nasal cavity, (Lacrimal duct is an anatomical drainage canal connects the corner of the eye to the lower surface of the nasal cavity).

Itching when wound heals:

49 Guidance for Children Itching when wound heals Itching is due to the release of a chemical substance, called histamine, which stimulates nerve endings. Histamine is a decarboeylated form of amino-acid histidine, a powerful vasodilator present in animal tissues. When tissues become inflamed, histamine is released from mast cells in the tissues. During healing, the number of basophils in WBCs increase. Basophils contain relatively large amounts of histamine. Histamine from the basophils and from the surrounding cells diffuse into the skin nearby and stimulates the nerve endings, which leads to itching.

Wound becomes Septic:

50 Guidance for Children Wound becomes Septic The reaction between metal sheets and air or other oxidising agents are the cause for rusting. Rust is a form of oxidised metal film forms on metallic surfaces. When these rusted metals make wounds, the micro-organisms gain entrance into the wounds as spores and germinate under unaerobic condition particularly when the wound is deep or if the oxygen tension is low due to the presence of other aerobic micro-organisms. During the metabolism these clostridia excretes toxins, that are pathogenic for human beings, the wound become septic and if left untreated results in death.

Burning Sensation using Dettol:

51 Guidance for Children Burning Sensation using Dettol Tincture, dettol and other similar antiseptics act as disinfectants and are corrosive in nature. When these antiseptics are applied on wounds, due to their corrosive nature they damage the cell proteins in the tissues. This action stimulates the underlying sensory nerves leading to a sense of irritation. To reduce the corrosive action, use them in a diluted form [live adding water to it].

Sleepy after heavy meals:

52 Guidance for Children Sleepy after heavy meals In the human body the mechanism is such that the oxygen we breathe in and the vital nutrients in the food that we eat are absorbed by the blood and supplied to the different organs. The amount of blood supplied to each organ depends on the oxygen and nutrition requirement of the tissues of the organ and the importance of the function it plays at any given time. Normally: one-third of blood goes to liver, one-fourth to kidney, one-sixth to brain. Remaining goes to the muscles and other parts of the body. With heavy meals, digestion of the food is needed and so more blood is sent to the stomach wells. Automatically the flow of blood to other parts of the body, including the brain, is reduced.

Yellowing of Urine:

53 Guidance for Children Yellowing of Urine Yellowing of urine is due to the predominant rise in the unconjugated bilirubin in the blood. Administration of certain drugs in the patients can also result in the rise of unconjugated bilirubin. Even some common medicines like paracetamol and sulfonamide are hepatotoxin. So they cause mild damage to the liver cells which results in the increase of bilirubin level in the blood. In the case of tonics, yellowing is due to excretion of B-complex vitamins. These vitamins are water soluble and absorption of these vitamins is very rapid. But they are rarely stored in liver except vitamin B-12.

Vegetables washing and cooking:

54 Guidance for Children Vegetables washing and cooking When the cut vegetables are washed in water, the water soluble vitamins (B complex and Vitamin C) are leached away. So, wash before cutting. When vegetables are cooked, thermal destruction of vitamins and nutrients also take place. So, over heating of vegetables should be avoided. Frying and roasting is bad as it causes 40 - 60 per cent nutrient loss.

Vomiting while Travelling:

55 Guidance for Children Vomiting while Travelling Giddiness occurs when we lose our sense of balance. The sensations perceived by the eye, inner ear, skin, muscles and joints help the body to know its stability. When we look down from a great height, abnormal visual signs are transmitted to the brain, without any corresponding information from other parts of the body. While looking out in a fixed direction while travelling in a bus, the eye sends fast changing visual signals to the brain. Such signals confuse the mechanism in the brain and lead to giddiness and vomiting.

Blind men with improved capabilities:

56 Guidance for Children Blind men with improved capabilities Scientists have found that the brain is plastic – meaning, the brain can rewire itself. This has proved beneficial to the handicapped. Researchers have demonstrated the process of brain rewiring using a technique called transcranial magnetic stimulation in which they apply a magnetic field to the skull and induce electric currents on the brain. They found that the visual cortex (the part of the brain which handles signals from the eye) of a blind person’s brain does not remain idle – other senses use it.

Atmosphere with stellar bodies:

57 Guidance for Children Atmosphere with stellar bodies Atmosphere of stellar bodies is determined by studying the spectrum of the light coming from the stellar body. We know that the atmosphere is made of atoms and molecules. Each of these atoms and molecules emit light at characteristic frequencies or wavelengths which are also called signatures. No two elements emit light of the same frequency. Researchers use spectroscopic tools to study the light coming from stellar objects and identify the frequency of components in them.

Stars blink but not planets:

58 Guidance for Children Stars blink but not planets The stars seem to twinkle, because we see the stars through the ocean of air, the atmosphere. The twinkling is caused by differences in temperature in the air. Some layers of air are hotter than others, and one layer is always swirling and moving through another. These different layers of air bend the star light in different ways, and at different angles. Stars near the horizon seem to twinkle much more than those high in the sky. This is because the light of these stars has to travel a longer path through a thicker layer of atmosphere, and thus has more chance to become disturb. More rays come to us from the surface of a planet than from the surface of a star. The light from the planets does not waver as much as that from the stars, the wavering of one ray of light is counteracted by the wavering of another ray in another direction.

Refrigerator sound:

59 Guidance for Children Refrigerator sound The sound from a fridge is due to the frequent switching on and switching off the compressor. The compressor is controlled by a thermostat, a device which is generally used to measure temperature. When the inside of the fridge reaches a present temperature, there is no need to cool it further. So, the thermostat sends a signal and cuts the power to the compressor to stop its cooling function. When temperature increases and reaches the critical temperature, the thermostat sends a signal to restore the circuit and switch on the compressor.

Cool room with fridge open:

60 Guidance for Children Cool room with fridge open Open fridge will heat the room. Under normal circumstances, the heat from inside the fridge is taken out by the compressor and let out in the air behind the fridge. If the fridge is kept open in a closed room, the chillness coming out through the front door of the fridge is cancelled by the heated air coming from behind. In any electrical appliance, a part of the electricity supplied is wasted as heat because of the principles of thermodynamics. This heat will raise the temperature of air inside the room.

Automatic wrist watches stop:

61 Guidance for Children Automatic wrist watches stop Automatic watches have a different mechanism: a rotor which can rotate freely (like a free wheel in a bicycle). Our hand movements make the rotor rotate and wind a coil spring. The rotor frees itself to the original position after the winding. As a result the rotations of the rotor tighten the spring. The watch works as the spring releases very slowly. If the watch (spring) is kept idle for some time, there is no rewinding of the spring, and so it stops functioning.

Pressure cooker:

62 Guidance for Children Pressure cooker Principle of a pressure cooker is cooking under increased pressure. It is well known that food gets cooked fast at high temperatures. There is no possibility of heating the water beyond 100 degrees in open vessels. Hence it takes a lot of time to cook the food. Boiling point increases with increase in pressure. Hence in pressure cookers, the steam in not allowed to escape but enclosed with in the vessel. As more water is converted into gaseous stream, the pressure increases which in a feed back mechanism increases the boiling point to well beyond 100 degrees enabling fast cooking. Normally the temperature reaches about 120 degrees inside the pressure cooker. In order that the pressure does not reach very high values so as to cause an explosion, a weight and safety valve are provided to let out the excess stream. Also the body of the cooker is made of an alloy which can withstand high pressures.

Draw more current with low voltages:

63 Guidance for Children Draw more current with low voltages Current and voltage are not always in direct proportion. Electrical appliances are divided into two groups: Appliances such as electric irons and electric heaters which convert electrical energy into heat energy. Appliances such as motors which convert electrical energy into mechanical energy. In first group, the current drawn is proportional to the square root of the voltage. In the second group, the current drawn is inversely proportional to the applied voltage, that is, when the applied voltage is lower, the current drawn will be proportionally higher, with the mechanical power remaining constant. Motors operating at low voltages burn out because they tend to draw unduly large currents which can not be carried by the wires wound inside them.

Earthing Pin is Bigger:

64 Guidance for Children Earthing Pin is Bigger Earth wire starts from the metal body of the appliance and ends in the earth. So it should never come into contact with live wire. In case the earth pin is connected wrongly with the live socket, the user touching the appliance might receive an electrical shock. Earthing pin is made longer than the other pins, so that it gets connected the earth terminal first before the other pins (live and neutral) make the contact in their respective sockets. In case there is a short circuit, as soon as the appliance is plugged in, the current from the electrical appliance flows to earth without harming the user. Hence it is always safe to install thick high tension wires for earthing.

High Tension Wires - humming sound:

65 Guidance for Children High Tension Wires - humming sound Air surrounding the conductors of a high voltage overhead transmission line is normally an insulator. But at extra high voltages (66,000 volts and above), the air in close proximity to the conductor tends to break down under the voltage stress, along the length of the conductor and itself becomes a conductor. This is known as corona effect. This effect is seen as bluish violet light and audible corona as a hum. Audible corona is common. Visual corona requires a higher voltage stress.

Electric Line Tester:

66 Guidance for Children Electric Line Tester It is used for testing alternating current (AC). In an electric line, ‘phase’ line gives out AC which has both positive and negative components. In the case of a tester, when we touch its metal cap, a very small amount of current being tested passes through the neon bulb, a high resistance and through the body to the earth which is at zero potential. In other words the body helps to complete the circuit enabling the tester to glow. The high resistance inside the tester acts as a safety mechanism by restricting the amount of current passing through the body.

Bird not get electrocuted:

67 Guidance for Children Bird not get electrocuted A bird sitting on a live wire will be electrocuted only if electric current passes through its body. One wire which we call live will be at a potential of 230 volts which is called the phase wire and the other one which we call the neutral wire will be at a potential of zero volts. Immediately on sitting on the live wire the bird’s potential will also be raised to 230 volts and if by an accident it comes in contact with the neutral wire or touches it, a current will pass through its body from the live wire which is at a higher potential to the neutral wire which is at zero potential.

Fan Wings Slightly Curved:

68 Guidance for Children Fan Wings Slightly Curved Fan wings, also called blades, are curved for optimum air circulation which is determined by solidity ratio which is the ratio of the area of the blades to the area of the disc swept by them. If a flat plate is used as a blade, it will provide air circulation no doubt but the volumetric flow will be less compared to a blade which is suitably curved based on an aerodynamic principles. The cross-section of a blade is in the form of a circular arc and is called camber. It will vary from the root of the blade to its tip. One can see the blade twisted from the root to the tip.

Reduce power with slow speed in fans:

69 Guidance for Children Reduce power with slow speed in fans We can save power with the new electronic regulators but not with the old regulators based on rheostats. Rheostats consume a fixed power all the time. If we select the highest speed all the power is fed to the fan’s motor. If a lower speed is selected, electric power proportional to selected level is fed to the motor and the remaining power tapped from the mains is wasted as heat in the rheostat. That’s why when we run the fan at slow speeds for a long time the regulator becomes hot. New regulators are made up of semiconductor device called triac. Depending on the speed selected, the electronic regulator draws, from the mains, only the required power.

Chokes and Starters in Tube lights:

70 Guidance for Children Chokes and Starters in Tube lights Tube lights are discharge lamps. To initiate a discharge, it requires a high voltage (about 1000 volts) several times the main voltage (about 200V). To sustain a discharge it requires only about 100 V. Choke in an inductance. When current through an inductance is abruptly interrupted it induces a high voltage. The interruption is done by the starter which works like a switch. The high voltage strikes an arc between the filaments at the ends of the tube light. Once an arc has struck, the choke takes half of the mains voltage and leaves the rest to maintain the arc. Choke has a core made of thin laminated silicon steel sheets. When the sheets vibrate with the power frequency (50 Hz) or its harmonics it generates noise. A starter is made of two electrodes one of them is a bimetallic strip. When a tube light is switched on, the voltage between the two electrodes produces a spark.

Incandescent light bulbs turn grey:

71 Guidance for Children Incandescent light bulbs turn grey The greying of the inner surfaces of incandescent bulbs is the result of gradual evaporation of tungsten from the filament while the light is on. This evaporation eventually makes the filament so thin it burns out. To reduce greying, a mixture of nitrogen and argon is used today. A small amount of abrasive tungsten powder can be placed in the bulb. Shaking it occasionally will remove the grey coating from the surface to the glass. Greying can almost eliminated by introducing a small amount of halogens iodine and bromine.

Shadows with tube light and lamps:

72 Guidance for Children Shadows with tube light and lamps As light travels only along straight line paths, if obstructed by any object, it creates a shadow. Filament bulbs are point sources, that is, the light emanates from almost a single point and goes out radially in all directions. In the case of filament bulbs, there is no light ray falling on the shadowed area and so the shadow is harp. If the light from one end of the tube light causes a shadow, there is a possibility for the shadowed area to be lit by a light rays coming from the other end or part of the bulb. Hence the shadow is blurred.


73 Guidance for Children Photocopier Photocopier is an electromechanical device having a photoconductive cylindrical drum made of cadmium, selenium or an organic photoconductive material. (A photoconductive material changes its conductivity under light). Upon switching on the machine, the drum is positively charged and the heating section, at the exit of the copier, with a teflon coated roller is heated to 230 to 320 degrees Celsius by a heating lamp. An image of the document is reflected by various mirrors and lenses to the drum. Depending on the intensity of the light received the photoconductive material loses its resistance at varying levels on its surface. That is, the positive charges on the drum are neutralised except in those areas representing the image. This results in a latent charge image on the drum. A toner (negatively charged) is then pumped to the drum. Based on the ‘charge map’ the toner gets deposited and forms a ‘toner image’ on the drum. The drum then rotates and prints this image on the moving paper and ‘fixes’ it at a high temperature.

Radio signals with directions:

74 Guidance for Children Radio signals with directions In radio sets, the problem of not receiving signals in certain directions is felt in the medium wave band. This is because for this band they use a coil wound on a ferrite rod as the antenna. Ferrite rod is directional in its sensitivity. It picks up all signals that come in a direction perpendicular to its axis and rejects them if they come parallel to its axis. Therefore the reception is entirely based on the direction in which they reach the radio set.

Gravel on Railway Tracks:

75 Guidance for Children Gravel on Railway Tracks Gravel used on railway tracks is known as ballast. It is used to dissipate the vibration produced by trains travelling at high speeds. In effect, the gravel layer acts as a cushion and damps the vibrations so that they do not travel long distances. If the rails are laid on a solid base, these vibrations can travel long distances and lead to cracks on the base as well as on nearby buildings.

No Sound in Vaccum but Light:

76 Guidance for Children No Sound in Vaccum but Light Sound is a mechanical wave but light is an electromagnetic (EM) wave. Mechanical vibrations propagate by the actual displacement of physical properties. Each particle oscillates about its mean position in a synchronized manner ot cause energy propagation in a mechanical wave pattern. In EM Waves, electric and magnetic fields ‘oscillate’ about their mean zero in mutually perpendicular planes and cause wave motion. Thus EM Waves doesn’t need a medium but Mechanical waves need a medium.

Different Rods in TV Antenna:

77 Guidance for Children Different Rods in TV Antenna The length of the elements and their arrangement depend on the wavelength of the signal (local TV station). For good reception, the antenna’s length should be half the wavelength of the signal in metres. The gain of the folded dipole antenna alone will not be much. To reflect the signal which are not intercepted by the dipole, a reflector of length more than half lamba is fitted at the rear end. It reflects the electromagnetic waves just as a mirror reflects light waves. Normally, only one reflector is used because additional reflectors do not significantly improve the gain. To boost the gain, the signal is directed towards the dipole using the director elements which are of length less than half lamba.

Water Heater Coil – Heating Process:

78 Guidance for Children Water Heater Coil – Heating Process Molecules of water that are adjacent to the heating coil first gets heated and thereby becomes less dense. The water of lesser density will move up due to which the high density cool water on the surface comes down. (Liquid of low density will always be at the top than a liquid of high density). This movement of water molecules causes water at the upper level to become warm sooner than the bottom level though we put the coil at the bottom.

Global Positioning System:

79 Guidance for Children Global Positioning System GPS is a system which shows the exact position on the earth, anytime in any weather and any where. There are 24 GPS satellites orbiting at 11,000 nautical miles above the earth. GPS has 3 parts: Space segment consists of 24 satellites. User segment consists of receivers which we can hold in hand or mount in a car and this gives the exact location on the earth. Control segment consists of ground stations that make sure that the satellites are working properly. Receiver detects the time signal and calculates the distance of the satellite. By getting signals from three different satellites and by doing mathematical calculations, the receiver is able to give the exact position where the receiver’s located.

Milk Overflows but not water:

80 Guidance for Children Milk Overflows but not water Milk is of water (83 – 87%), protein (3.5%), sugar (5%) and fat (4 – 7.4%). When milk is heated, fat boils lighter than water, floats as a creamy layer on the top and water vapour, in the form of steam bubbles, is trapped under it. Further heating results in the formation of more number of bubbles. These bubbles expand and lift the creamy layer causing it to overflow. In the case of water, the steam bubbles break as they reach the surface.

Candle lights a room but no LPG:

81 Guidance for Children Candle lights a room but no LPG Yellow light in candle is responsible for illumination of the room. Combustion (burning of fuel) can be of two types: Complete: Sufficient quantity of oxygen for the fuel to burn. This results in a blue frame and the heat generated will be maximum. Incomplete: Oxygen supply is insufficient. This results in an yellow frame with heat produced is lesser than maximum obtainable from the fuel. Candle flame has blue [hottest zone surrounding the wick], black [unburnt volatile fuel] and yellow flames. Yellow flame has hot carbon particles which get heated by hotter zones below and emit light due to incandescence. LPG (Liquified Petroleum Gas), which is mostly propane and a little butane, is mixed with sufficient quantities of air in the burner and then burnt to give a blue flame. Propane needs about 25 times its volume for complete combustion. The flow of gas in controlled and ratio of gas and air is maintained. As there is no incandescent zone, the flame does not illuminate the room.

Information on Audio & Video Tapes:

82 Guidance for Children Information on Audio & Video Tapes Information is stored in audio/video tapes by magnetizing them. These tapes are actually long, thin plastic films coated with a magnetic material, mainly iron oxide. Player has a recording head which consists of a coil of a wire wound around a circular piece of iron with a small gap. Any current passing through the wire would produce a magnetic field around it. When the tape is run through the small gap present in the recording head, the varying magnetic field magnetism the particles on the tap rearranged their moments in accordance with the variation in the input signal. While playing, the tapes is run past the recording/playing head which senses the magnetic field along the tape. This induces a varying current in the coil . This current is amplified and fed to the speaker or TV to reproduce the original message.

Popping Ears in Aeroplane:

83 Guidance for Children Popping Ears in Aeroplane To maintain fuel economy, aircrafts should fly at altitudes far in excess of those capable of sustaining life. Whereas 5500m is about the maximum altitude at which a person can live for any extended period, a subsonic passenger jet has the best fuel economy when flying at around 12000m. Therefore, aircrafts have to be pressurised the interior of a passenger aircraft. All airfields are not at the same altitude. As for ear popping, for our safety and comfort the internal pressure is imperceptibly reduced, all under computer control, as the aircraft climbs. It is gradually increased during descent so that, as the aircraft is coming to a stop on the runaway, the pressure inside and out is the same. Normally, it is sufficient for your ears to adjust. If not, pinch your nose and gently but firmly increase the pressure in the nasal cavity until you feel the pressure equalise.

Cola Foam Up:

84 Guidance for Children Cola Foam Up Carbonated beverages when opened and released from pressure or supersaturated solutions of gas with more carbon dioxide dissolved in the beverage than would be possible at normal pressure. Left alone for two hours, the drink would slowly lose the gas and go flat. Sodium chloride particles seem to provide an especially good surface for gas to collect on, form bubbles and quickly rise to the surface and escape.

Ornaments of Pure Gold:

85 Guidance for Children Ornaments of Pure Gold Ornaments could be made of pure gold but would get easily pressed out of shape. This is because gold is a soft metal, though it is heavy. Gold has high density, over two times that of iron, because its atoms are heavier. A steel knife cannot cut glass, but a diamond tipped steel knife could, because diamond is harder than glass and steel is not. Gold is easily scratched. A bit of copper is added to gold, to give the ornaments hardness and to prevent distortion. 24 carat means 100 per cent gold. One carat represents 100/24 per cent. 22 carat gold means 91.76 per cent of gold. Rest is copper.

Hard Water and Layer on Utensils:

86 Guidance for Children Hard Water and Layer on Utensils Water contains dissolved salts of calcium, magnesium and often iron in the form of bicarbonates, chlorides and sulphates present in the Earth’s crust. When such water is heated, the bicarbonates of calcium and magnesium decompose evolving carbon dioxide and leave behind sparingly soluble carbonates. Bicarbonates of iron interacts with the carbon dioxide and water forming sparingly soluble ferric hydroxide (brown). These sparingly soluble salts form the layer or ‘scales’ seen in utensils and boilers.

Cold water extinguish fire faster:

87 Guidance for Children Cold water extinguish fire faster If we use hot water to extinguish fire, the heat absorbed from the source (fire), by a definite quantity, to reach its boiling point will be far lesser vis-à-vis the same quantity of cold water. Colder the water, faster would be extinction of the fire.

Boiled Water lose Taste:

88 Guidance for Children Boiled Water lose Taste Natural water contains few substances [gases like oxygen, carbon dioxide, sulphates and carbonates of calcium and magnesium, iron, etc] that impart not only taste but also hardness to it. Due to boiling, the dissolved gases are released and hardness is removed. Insoluble carbonates and hydroxides are formed which get deposited on the surfaces and the bottom of the vessel as scales. Their separation from water deprives it of its taste.

Air-Cooler and Air-Conditioner:

89 Guidance for Children Air-Cooler and Air-Conditioner Air conditioning system is the system which keeps on control and maintain the particular condition (this is required temperature and humidity of air) in the closed space. It is technically defined as a system which controls temperature, humidity, purity and motion of air to produce desired effects upon the occupants of the space. In case of air cooler, which has the capability to cool the air inside the space does not maintain particular temperature and humidity of that air. In response to atmospheric seasons we can have winter, or summer air-conditioning system, but any air cooler will not do so.

Black box in Aeroplanes:

90 Guidance for Children Black box in Aeroplanes Black boxes which usually hold the clues to a plane’s crash, are built strong enough to survive bomb blasts, violent impacts and intense fires. They measure approximately 4 by 6 by 8 inches and weigh about 30 Kg and are kept in a case which can withstand 30 minutes of 1100 degrees C at 50,000 (Btu’s) British Thermal Units per square foot per hour. Actually orange in colour and a very high quality heat resistant paint is used, so that they can be spotted easily even at dimly lit crash sites. They are always places in the tail end of the flight. Black box records voice and flight data. Cockpit voice recorder: Collects data and retains a record of the most recent 30 minutes, the conversation between the pilot and Ground Control Room. Flight data recorder: Records most recent 25 hours of a plane’s operating data, including altitude, air speed, vertical acceleration and heading.

Biscuits loose crispness in cool air:

91 Guidance for Children Biscuits loose crispness in cool air Moisture content in fresh biscuits is about five per cent after baking resulting in crisp texture and good storage stability. When they are left open in air, they absorb moisture and lose their crispness. The relative humidity in the atmosphere can vary from about 40 per cent (during summer) to 90 per cent (on a cool, rainy day). Inside a fridge, the temperature is kept low by cooling the air. The water molecules present inside the fridge condense on the cooling coils (evaporator coils) and so the humidity is also low (the air is moisture-free). The moisture appears as frost. As a result the biscuits remain cool as well as crisp.

Layer on top of hot beverages:

92 Guidance for Children Layer on top of hot beverages The layer that forms on top of hot beverages consists of fat. In unheated milk the fat globules are surrounded by a thin film of protein, phospholipids and neutral fats. When the milk is heated, this thin film breaks, making the fat globules free. These then coalesce on the surface which then come to contact with the air and forms a layer.

Beverages of Feeling fresh:

93 Guidance for Children Beverages of Feeling fresh Most of the beverages contain alkaloids which act as mild stimulants. Caffeine in Coffee, Theophylline in Tea, Cocaine in Coco Products. These alkaloids are collectively referred to as methyl xanthines. They share a number of pharmacological actions of much therapeutic interest: they relax, smoothen the muscles (notably bronchial muscle), and stimulate the central nervous system and cardiac muscle. They induce the kidneys to excrete more urine, stimulate mental activity, quicken the reflexes, increase vigilance and decrease motor reactions time in response to both visual and auditory stimuli. They increase stamina and reduce fatigue. They give the users a feeling of confidence and power. They even induce euphoria in some users. These stimulant effects a short lived: they last for about an hour. They are then subsequently followed by depression.

Pencil Eraser:

94 Guidance for Children Pencil Eraser A pencil mark actually consists of graphite particles abraded from the pencil point by the paper. These particles, which have an angular, gritty look under the microscope are, for an HB lead pencil, typically between 2 and 10 micrometres in diameter. The particles lie slightly below the surface of the paper, interlocked between its fibres. A single rub using a rubber sufficiently soft to reach between the fibres will pick up most of them. Inspection of the rubber shows the undamaged particles adhering to the surface. An effective erasing material is also abraded by the paper surface, producing the familiar small spindles of rubber or eraser material, which wrap up the graphite particles.

Stick to walk on ropes:

95 Guidance for Children Stick to walk on ropes While walking on a rope, as the base is very thin (as thin as the rope), to be stable the artist has to move his centre of gravity appropriately. This he does by holding a bamboo pole horizontally or using an umbrella or just by spreading his hands? When the artist feels that he is falling to his left, he moves the pole to his right (and vice versa) and counters the forces disturbing his balance and makes the centre of gravity fall within his base.

Mehndhi impart color:

96 Guidance for Children Mehndhi impart color Human skin is made of four layers – the tipmost layer is stratum corneum, followed by epidermis, dermis and sub-cutaneous layers. When mehndhi is applied on the skin, the red pigments present in it are transported along with water through the small pores in the stratum corneum. As the hand dries, the water evaporates leaving the pigments which impart the colour. In nails, the pigments are trapped between the horny plate like cells which are piled in lamellar layers. Pores in skin are larger than those in nails. This actually accounts for rapid fading of colour in skin compared to that of the nail.

Blind Feeling in Dark Room:

97 Guidance for Children Blind Feeling in Dark Room Seeing in dark involves two types of cells – rods and cones, in the eye. These cells are present in the light-sensitive innermost layer of the eye called the retina. They lie in front of a pigmented tissue layer. Cones are present in the area of greatest visual activity – fovea centralis, which lies at the centre of small yellow pigment spot behind the pupil. Rods and cones are present around the fovea. Cones are active under intense illumination, whereas rods are active in dim light. In the dark, rods are sensitised by a pigment called rhodopsin or the visual puple that is formed within the rods. Rhodopsin is bleached by light and is reformed by the rods in darkness. Hence a person who steps from sunlight into a dark room experiences a blinding feeling till the pigments being to form. Cones adapt themselves to fainter light in the ambience of low intensity illumination, which may take around five minutes.

Closing Wooden Doors in Winter:

98 Guidance for Children Closing Wooden Doors in Winter When dry wooden pieces and seeds of certain species are put in water, they absorb water and swell noticeably. This phenomenon of water absorption is called imbibition. Imbibition is due to the presence of large number of hydrophilic colloids in both the living and dead cells of wooden materials. During rains, relative humidity of atmosphere air is high. Hence, wooden doors absorb water molecules and swell. If the clearance between the door frame and door is insufficient to accommodate the swell, we experience difficulty in closing and opening it. Periodic painting helps to reduce moisture absorption and the difficulty.

Glass Tumbler breaks with Hot Water:

99 Guidance for Children Glass Tumbler breaks with Hot Water Glass tumblers break due to the difference in thermal expansion of their inner and outer surfaces. Glass is known as a bad conductor of heat. Hence when the tumbler is suddenly filled with hot water, the inner layer of glass gets heated immediately as it comes into contact with the hot liquid. But the outer layer remains at a lower temperature for some more time as the heat is conducted through the glass only slowly. As a result, the inner layer tends to expand more than the outer layer. This leads to cracking. Thick-walled tumblers and tumblers made of special quality glass withstand such cracking to a certain extent.

Noise Shatter Glass:

100 Guidance for Children Noise Shatter Glass Noise (a mixture of sound waves of varying frequencies) generated by the vehicle sets up vibrations in the atmospheric air surrounding it. These vibrations (sound waves) transfer the energy from the source (vehicle) to the surrounding and dissipate it. If the noise is not intense, the sound dies away with in a short distance. If it is intense, the waves travel long distances. When these waves come across solid objects such as window panes, they transfer their energy to the object and force them to vibrate. If the frequency of the sound wave matches with the natural frequency (Any object will have a natural frequency of vibration which depends on the nature of the material) of the object, resonance sets in the object begins to absorb the incident energy and forced to vibrate with large amplitudes. In case of window panes, its edges are held (if not tightly) by the window frame which prevent the oscillation. This results in shattering.

Shaving Brush Give More Lather:

101 Guidance for Children Shaving Brush Give More Lather The bristles of a shaving brush are bunched together to ensure that there are a large number of thin columns of air in-between them. When the brush is moved to and fro, the soap solution seeps into the brush, due to surface tension, partially filling the air columns. While shaving, the soap solution stuck to the skin is dragged to from thin films. But when stretched beyond a certain length, limited by surface tension, the films break and in that process trap a little bit of air to form small bubbles. As there are hundreds of bristles involved in the bubble making process, we get lather within a short time. The same principle applies to tooth brush and the brushes used for washing.

Verify Purity of Honey:

102 Guidance for Children Verify Purity of Honey Honey is adulterated by way of adding jaggery syrup. To verify whether honey is pure, take a glass of waterand pour one tablespoon of honey in it. Gently shake the glass (note not to stir). If the honey completely dissolves in water it is adulterated. On the other hand if it stays as a mass, it is pure honey.

Kite Flies but not Paper:

103 Guidance for Children Kite Flies but not Paper Obviously because of the string and the tail. First, the sheet of paper is made stiff using thin sticks so that it does not bend due to the forces of the wind. Next, 3 – 4 small strings of equal length are attached. All this is to make the kite fly at an angle with the direction of the wind. Force acts in two components – one horizontal and the other vertical. Generally, the vertical component lifts the object (against gravity) and the horizontal component pushes the object (along the direction of the force). Here the force acting on the kite is due to the wind. In kite: kite is held by string in one direction (a restoring force) and the wind is exerting its force in opposite direction. At times we pull the string or run into the wind. These are tricks to increase the lifting force and make the kite fly higher. Some kites tend to rotate along the axis of the string. To prevent this rotation, a long tail is attached.

Aeroplanes and lightning:

104 Guidance for Children Aeroplanes and lightning Clouds are made of water droplets and dust in the atmosphere at altitudes of 1 to 16 Km. While travelling through air, due to friction, the water droplets get electrically charged. Lightning occurs due to sparking between oppositely charged clouds – a high voltage spark rushes towards the ground (at zero potential) through moisture filled air. If any ground based structure is on the path of the spark, the top of that structure is excited to a high electrical potential while its bottom (in contact with the ground) remains at zero voltage. This high potential difference sets a very high current in the structure causing sudden heat generation in the material and destruction. But in flying aeroplanes, there is nothing like a ground point which remains always at zero voltage. Thus if hit by lightning, the plane’s entire surface acquires same high potential and due to lack of potential difference there is no current and so no destruction.

Blotting Paper Absorb Ink:

105 Guidance for Children Blotting Paper Absorb Ink Blotting paper absorbs ink by capillary action which is a natural phenomenon exhibited by liquids in the attempts to reduce surface tension. Blotting paper is made of cellulose obtained from the pulp of cotton linter, wood or straw. A purified pulp paste is directly pressed to form blotting paper sheets without any treatment. So as to incorporate microscopic capillaries. When such a paper is placed in ink, water or any aqueous solution, the solution immediately enter in to these capillaries and spreads all over the sheet.

Train Stops when Chain is pulled:

106 Guidance for Children Train Stops when Chain is pulled Trains are equipped with vacuum brakes. Pipes passing through the underside of coaches are connected to vacuum cylinders (provided in the coach) which help maintain a vacuum throughout the length of the pipe. The pipes (of each coach) are then linked. When the driver wants to stop the train, he gradually allows air to enter the vacuum pipe and activates the pistons of the vacuum cylinders which help to apply the brake. For emergency application of brakes by passengers, coaches are provided with alarm chains connected to the vacuum system. When the chain is pulled, a small valve opens up and allows air to enter the system slowly, gradual application of the brakes. Direct admission valves are provided in each coach near the vacuum cylinder and they help in the uniform application of the brake throughout the train.

Sound with Thumb and Middle Finger:

107 Guidance for Children Sound with Thumb and Middle Finger A small amount of air is trapped and pressurised when the fixed end of the thumb and the free end of the middle finger are brought together. When this pressurised air is released suddenly during the clicking, it produces a sound as in the case of a balloon burst.

Watching TV:

108 Guidance for Children Watching TV If one sits too close to the television or cinema screen, the eye lens has to do more frequent focussing for viewing. Light rays from a near portion of the picture diverge and so the lens is curved more to focus on them. Simultaneously, the lens has to collect the light (coming more parallely) from more distant parts of the picture. This causes strain on the eye, and if practised for long, can permanently damage the eye. Width-to-height ratio of TV screen is kept as 4:3 because of the binocular vision due to the pair of eyes in the horizontal plane and the range of movement of both the eyeballs being less restricted in the horizontal plane as compared to that in the vertical plane. The best viewing distance for watching TV is 4-8 times the height of the screen.

Hearing Audio when TV Switched on:

109 Guidance for Children Hearing Audio when TV Switched on When TV is switched on, electric power is supplied to both audio and video sections. The video section consists of a cathode ray tube which is called as picture tube. An electron beam is used to sweep the screen to display the pictures. This electron beam is generated within the CRT using a filament which can emit electrons only when heated. This heating process requires some time. Audio section does not need any such ‘warm up’ to start functioning and so we hear the sound as soon as we switch on.

Tear Gas:

110 Guidance for Children Tear Gas Tear gas is a noxious gas. It is also called as war gas since it is used to disperse soldiers in a battle and an attacking mob. It is one kind of Lachrymator. Firing certain chemicals in artilleries or pen gun produces it. The chemical substance used is, either alpha chloracetatophenone, a solid material or ethyliodoacetate, a liquid material. Tea gas vapours cause irritation of eyes in with a copious flow of tears, spasm of eye lids and temporary blindness. Persons exposed to tear gas should be removed to fresh air and they should wash their eyes with normal saline or boric acid solution. Weak sodium bicarbonate solution should be applied to the affected parts of the skin.

Not to drink distilled water:

111 Guidance for Children Not to drink distilled water Distilled water contains some dissolved gases like carbon dioxide. Distilled water as such is harmful, if drunk. Because it contains no dissolved materials, it has a tendency to dissolve the tender mucous membranes on our mouth, etc. Warm water, especially if it is free of dissolved materials, will have a corrosive action on the delicate mucous membranes.

Changing water in aquarium:

112 Guidance for Children Changing water in aquarium Fishes use their grills to separate the oxygen from water and release out carbon dioxide. In lake or pond, there is not much considerable change in Oxygen level because: in a huge amount of water only negligible ratio of oxygen is used. Direct and indirect rainwater keeps the oxygen ratio stable. Water plants like Hydrilla and Vallisneria use the carbon dioxide and deliver oxygen during their photosynthetic activity. But in aquarium, there is less amount of water and there are not natural plants to maintain the oxygen level. Another reason for changing the water is to keep the water clean from the fish waste in aquarium.

Water Inside Coconut:

113 Guidance for Children Water Inside Coconut Coconut water is the endosperm part of the coconut plant. In a very young coconut fruit, the endosperm is found as a clear fluid in which float numerous nuclei of various sizes. This fluid is compactly filling the embryo sac in which the embryo is developing. At a later stage, free nuclei start settling at the periphery of the cavity and layers of cellular endosperm start appearing. This forms the coconut meat. This meat is very tender enclosing the fluid content called coconut water. It is called tender coconut. The quantity of cellular endosperm increases further by the division of cells. In mature coconut the liquid endosperm becomes milky enclosed by the cellular part called kernel and it does not contain free nuclei or cells.

Energy of raw and boiled rice:

114 Guidance for Children Energy of raw and boiled rice Energy content of raw rice is 3620 cal/kg with 12 per cent water content whereas that of boiled (cooked) rice is 1098 cal/kg with 73 per cent water content. Parboiled rice: Parboiling is a hydrothermal treatment followed by drying before milling for the production of milled parboiled grain. During parboiling, the B vitamins and minerals from hulls, bran and germ will be leached into endosperm and hence loss during polishing is minimised. Energy content of parboiled raw rice is 3703 cal/kg with 10 per cent water content whereas that of boiled (cooked) parboiled rice is 1057 cal/kg with 73 per cent water content.

Refrigeration and Freshness:

115 Guidance for Children Refrigeration and Freshness Vegetables when allowed to stand for a long period after gathering, they become wilted through loss of moisture by transpiration. This process affects the commercial and physiological deterioration of fruits and vegetables after harvest. Moisture loss adversely affects the appearance, texture, flavour and weight of the products. Tropical vegetables and a variety of greens should be stored between 8 and 12 0 C. At this temperature, the rate of metabolism of these vegetables is still considerably high, which reduces both quality and storage life. So refrigerated storage should be well supplemented with Modified Atmospheric Packaging (MAP). User perforated poly-packages that can maintain desired oxygen and carbon dioxide within the packages. Commercial storage of fruits require 0 0 C with preferred relative humidity of 85%. Fruits stored in home refrigerators tend to lose moisture. To prevent this, the fruits must be kept in ventilated covered containers, enabling the circulation of air around sides, tops and bottom of the fruits.

Mouth Sink After Sleep:

116 Guidance for Children Mouth Sink After Sleep Bad breath or ‘Halitosis’ is a common problem, which often occurs due to bacterial activity in the mouth. Halitosis, also termed ‘oral malodour’ is a foul or offensive odour emanating from the oral cavity. Local source of mouth odour is mainly the tongue. Post natal drip on the back of the tongue which occurs during sleep can also cause oral malodour in the mornings and can cause throat infections in some cases. A coated tongue is also said to be a cause of halitosis, due to excessive bacterial activity on the tongue. The cause of bad divided into Intraoral sources (sources inside the mouth which can cause bad breath), Extraoral sources (sources outside the mouth or anywhere else in the body). Intraoral sources include retention of odoriferous food particles on and between the teeth, coated tongue and dehydration states which can cause dryness of mouth leading to oral malodour caries. Periodontitis (inflammation of the tissues surrounding the teeth) is one condition if left untreated can cause bad breath from accumulated debris and increased rate of putrefaction of the saliva.

Humans Brush But Animals Don’t:

117 Guidance for Children Humans Brush But Animals Don’t Teeth are hard white structures found in the mouth of humans and in many other animals and are usually used for mastication. Animals need not brush their teeth due to the adaptation of their teeth. For eg., the teeth of snakes are very thin and sharp and usually curve backward. They function in capturing the prey and not in chewing. The teeth of carnivorous mammals for eg. Cats and dogs are more pointed and adapted to cutting and shearing. For carnivorous animals, chewing is not essential. Their teeth come into play only during cutting and shearing their prey. Animals cells in meat are not encased in cell walls and can be acted upon by digestive enzymes.

Drink Of Marine Mammals:

118 Guidance for Children Drink Of Marine Mammals Marine mammals do not actually drink. They get all their water from the fish that they eat. They come dehydrated very quickly if they are not feeding adequately and, when in captivity or care, they must be fed from a pipe or bottle if they are not eating.

Astronauts breathe in space:

119 Guidance for Children Astronauts breathe in space People on the space station get oxygen for breathing in two ways. The first way is to make oxygen from water by zapping it with electricity (electrolysis). Each molecule of water contains two hydrogen atoms and one oxygen atom. Running a current through water causes these atoms to separate and recombine as gaseous hydrogen (H 2 ) and oxygen (O 2 ). This makes oxygen gas and also hydrogen gas. The other way is from large tanks of compressed oxygen mounted on the outside of the airlock module of space station. While astronauts moving out from the space station use standard, off-the-shelf breathing air devices incorporated inself-contained totally encapsulating suits. They also breathe using ‘perchlorate candles’, which produce oxygen via chemical reactions inside a metal canister. (‘Perchlorate’ is packed inside the canister). Each canister releases enough oxygen for one person for one day.

Feel Sleepy while Reading:

120 Guidance for Children Feel Sleepy while Reading Feeling sleepy while reading for many is due to the posture in which they read. While reading a person rarely moves, this lack of physical activity causes decreased blood flow of muscles, which results in accumulation of lactic acid (a product of incomplete combustion in the cells). This lactic acid is a highly reducing or oxygen absorbing agent, which quickly reacts with oxygenated blood. This ensures lack of oxygenated blood flowing to the brain, which makes us feel sleepy. To tackle this problem we must avoid reading in a single stretch, instead its better to take some breaks and indulge in physical activity at short intervals.


121 Guidance for Children Anti-Perspirants Perspiration, or sweat, is our body’s way of cooling itself, whether that extra heat comes from hardworking muscles or from overstimulated nerves. Sweat does not ‘stink’ but it is only after bacteria eat the sweat that this excretions ‘stink’. Deodorants mask the smell of body odour, which is actually caused by bacteria, whereas anti-perspirants block the pores of the skin to stop us from perspiring. Most antiperspirants contain aluminium chlorohydrate/aluminium chloride or aluminium zirconium, which are highly soluble and readily absorbed into the skin. Once in the body, the aluminium passes freely across cell membranes and is readily absorbed. When the aluminium ions are drawn into the cells, water passes in with them. As more water flows in, the cells begin to swell, squeezing the ducts closed so that sweat cannot get out.

Eau-do-Cologne and Fever:

122 Guidance for Children Eau-do-Cologne and Fever We have temperature signals in the peripheral areas of our body. These areas are found especially in the skin and certain deep body tissues. These centres contribute very significantly to body temperature regulation. Set point is the particular temperature at which sweating begins. Hypothalamic temperature or core temperature is 36.7 to 37 0 C, when skin temperature is 33 0 C. When the skin temperature rises above this, due to warm weather and other reasons, immediately sweating begins. So when the skin temperature is very high sweating begins at a lower core temperature. On the other hand, during high fever both the skin temperature and core temperature begin to rise. Skin temperature will be above 330C and core temperature will be above 370C. Sine the core temperature is above normal sweating will not occur and so there will not be loss of body heat. But when the skin temperature is reduced to 290C we can induce sweating even at much high core temperature. This can be done artificially by applying eau-de-cologne, which is a cooling agent.

Temperature of Planets & Stars:

123 Guidance for Children Temperature of Planets & Stars Astronomers now take the entire electromagnetic spectrum into account, not just visible light. In general, cool objects give off radiation of long wavelengths while hotter objects give off short wavelengths. Infrared telescopes sent into space far beyond the obscuring atmosphere of Earth measure the short wavelengths below those of red visible light, and X-ray and gamma ray telescopes are trained on longer and longer, and hotter and hotter, astronomical objects and events.

Humming in Thermos Flasks:

124 Guidance for Children Humming in Thermos Flasks Humming sound heard in thermos flasks is due to the phenomenon of resonance. Background noise present in the atmospheric air acts as a source of energy (sound energy). Physicists call this as white noise as it is a mixture of all possible frequencies ranging from 20 Hz to 20 kHz which are audible to us. This noise may not be audible to us because of their very low intensity. When these sound waves encounter a cavity like that of a flask they are ‘filtered’, that is, only sounds of particular frequencies (determined by the inner dimensions of the flask) are allowed to enter freely into the flask’s cavity, and other sounds are simply reflected in the outside. Hemoltz resonator is an acoustic device used to pick up and amplify a particular frequency equal to its own natural frequency from a mixture of sounds. Flask has very little damping factor (because of its highly polished inner surface) and so vibrations get reflected inside without much loos of energy. Due to resonance, this particular sound wave gets amplified and becomes audible.

Immediately switch on and off:

125 Guidance for Children Immediately switch on and off Don’t switch on immediately after switch off. In fridge: Expansion device that changes the pressure refrigerant into low pressure is a simple capillary tube. When the fridge is switched off the compressor stops working and the refrigerants slowly down to the evaporator. If the system is switched on immediately, the compressor starts under ‘no load’ condition. Refrigerator uses low-power motors along with compressors to reduce cost. A small wait period (a few seconds) is needed to allow all the refrigerant to flow into the evaporator. In TV: Problems arise due to transformer which holds a stray magnetic field for a short duration, even after switch off. If we switch it on immediately, the field set up by the power supply will interfere with the stray magnetic field and reduce the efficiency and the life of appliance. With a few seconds wait period, this could be avoided.

Refrigerator Capacity in Litres:

126 Guidance for Children Refrigerator Capacity in Litres Capacity means the place occupied by a certain thing. Usually weight of different things/items will not agree with the same capacity. i.e., weight of 250 litres of water is less than the weight of 250 litres of oil. However if they are poured into a container of 250 litres, they would occupy the full container. Hence capacity is concerned with the place occupied by the things and not with their weight.

Vehicle Crossing and Flickering TV:

127 Guidance for Children Vehicle Crossing and Flickering TV Two wire transmission line has two wires of conducting material running parallel to each with air as the dielectric mediate. The waves travelling through this are electromagnetic in nature. So when a vehicle (having spark plug) crosses the place the spark from the plug creates an electrical disturbance. This electrical wave interferes with the electromagnetic wave in the transmission line and as a result one gets disturbances on the screen. In coaxial cable (used by satellite TV channels), inner and outer conductors are separated by a solid dielectric media. So when the electrical disturbance from a vehicle interferes with the electromagnetic waves in the cable they reach the outer conductor easily but when the passing onto the inner conductor they are offered a resistance by the dielectric media (mostly mica).

Lightning affect TVs:

128 Guidance for Children Lightning affect TVs Lightning is actually a sudden discharge of high voltage and high current arising out of large voltage (potential) differences between charged clouds. These surges, in their path towards the earth, can strike power lines and antenna and pass through the wires to terminal equipment such as TV. Huge currents and voltages, even though of short life, can damage the electrical components and electronic circuits which are usually designed for low power. The surges are so powerful that they can destroy the equipment even if they are off but connected to the mains/antenna.

Electric Current Causes Death:

129 Guidance for Children Electric Current Causes Death Electrocution depends on the amount of current that flows through or over the body. High voltages (higher tensions) may cause the person to be thrown, while lower tensions, around 240 volts, cause muscle contraction due to which person holds on to the source of the current. This is also dangerous, because severity is directly proportional to the duration of current flow. Dry skin offer high resistance but the resistance is diminished when the skin is moist or covered with sweat. Blood has a low resistance and as such within the body, electricity tends to be conducted along blood vessels. The intense heat, which may results from flash over produces burns. High voltage burns may be severe with charring of the body. If the area of contact is relatively large, e.g. when a hot wire is grasped with a wet hand or when a person is electrocuted in a bath tub, death may occur without any visible skin burning. Electrocution also depends on the path of the current in our body. Death is more likely to occur if the brain stem or heart is in the direct path of the current.

SIM Card Function in Cell phone:

130 Guidance for Children SIM Card Function in Cell phone It is a plastic card, which is called a subscriber identity module (SIM). It consists of an integrated microprocessor chip, which keeps data relating to a subscriber, and provides communication with GSM network. All GSM cellular communication telephone cells are performed via these antenna and stations, which are regulated by switching centre. Switching centre provides communication between city telephone network, base stations and other cellular communication operators. Every time you switch on your cell phone, the communication is performed with the nearest base station. At the same time permanent receive-transmission of signals from your terminal is performed. SIM card serial number is printed on its backside. This number contains the information necessary to obtain a new card, in case SIM card or GSM phone is lot or stolen.

HAM Radio:

131 Guidance for Children HAM Radio HAM operators are amateur radio operators duly licensed by the government to operate their own small wireless transmitters purely as a hobby to develop their scientific skill particularly in wireless communication and not for any pecuniary benefit. To be a ham, we need to pass an exam in basic electronics, operational procedure and Morse code conducted by Ministry of Communication, Government of India. Each one is assigned a distinct number called ‘call sign’. Short wave communication is one the important findings of amateur radio operators. One can monitor the conversation between hams using an ordinary radio set at 7 MHz frequency (41 metre band).

Diamond Sparkle more than Glass:

132 Guidance for Children Diamond Sparkle more than Glass This is a phenomenon of total internal reflection of light, dependent on the ‘critical angle’ of the incidence of light in a material medium at its bounding surface with air. When a ray of light travels from a denser medium to a rarer medium, the refracted or deviated ray is bent away from the normal (perpendicular) on the interface of the two media. For a certain angle of incidence, the refracted ray becomes parallel to the bounding surface or angle of refraction is 90 degrees. This angle of incidence is called critical angle. When the angle of incidence is further increased the ray is totally reflected back in the denser medium. This phenomenon is called total internal reflection. The higher the refractive index of a transparent material the smaller is the critical angle and hence the larger is the range of angles of incidence of more light to be totally reflected. A diamond has a large refractive index and very small critical angle as against glass. Light entering diamond from different faces, suffers multiple total internal reflection and comes out of the diamond as intense beams from selected directions. Hence, the diamond shines brilliantly.

Touch Screen Works – 1 of 2:

133 Guidance for Children Touch Screen Works – 1 of 2 You can use your finger on the computer screen to navigate through the contents. A basic touch screen has three main components: a touch sensor, a controller, and a software driver. The touch screen is an input device, so it needs to be combined with a display and a PC to make a complete touch input system. Three systems: Resistive: Made of Conductive and Resistive metallic layers with spaces in between. Electric current runs through them when monitor is operational. Change in electric field is used to find the location. Only 75 per cent of light from the monitor is transmitted.

Touch Screen Works – 2 of 2:

134 Guidance for Children Touch Screen Works – 2 of 2 Three systems: [Contd …] Capacitive: When we touch, some of the charge is transferred to the user, so the charge on capacitive layer decreases. Measuring the decrease in circuits located at each corner of the monitor helps finding the location. 90 per cent of the light from the monitor is transmitted and so brighter than the Resistive system. Surface Acoustic wave: Has two transducers (one receiving and one sending) placed along x and y axes of the monitor’s glass plate. Also placed on the glass are reflectors – they reflect an electrical signal sent from one transducer to the other. 100 per cent of light from the monitor is transmitted.

Sea Water Salty:

135 Guidance for Children Sea Water Salty Most of the rivers and streams empty themselves into it. The rivers are strewn with rock and plant debris. The rocks contain many minerals and salts (especially sodium chloride) which dissolve in the water. As the rivers drain into the sea, a considerable amount of salt gets dissolved in sea water. When these waters evaporate due to the heat of the Sun, they leave the salt behind. The evaporated water is brought back to the land in the form of rain and the rivers carry the water again to the sea. As this cycle is repeated, the amount of salt increases but the water content remains the same.

People Sweat before Heavy Rain:

136 Guidance for Children People Sweat before Heavy Rain Sweating, also called perspiration, is a continuous process. As the sweat glands, present below the skin secrete sweat, it evaporates into the atmospheric air depending on the humidity (moisture content) of the air. If the air is dry (low humidity) the evaporation is fast. But, before rain, the atmospheric air is saturated with water vapour and so the evaporation of sweat slows down. As a result with sweat accumulates on the skin giving us a feeling that we sweat more.

Condensed Milk & Fat:

137 Guidance for Children Condensed Milk & Fat Fat is an important constituent of milk. Cow’s milk should contain a minimum fat of 3.5 per cent and buffallo’s milk 6 per cent. Actually the fat content varies from breed to bread, and among individual animals. In Condensed milk, water is removed by evaporation in vacuum. Condensed milk is also prepared from skim milk (defatted milk) by concentration again with or without sugar. Condensed milk prepared from full cream milk (fresh milk) contains the same amount of fat present in ordinary milk. This is because by concentration, only the volume of milk alone is reduced. Purpose of condense milk is to reduce the volume of milk to enable long-distance transport and improve shelf-life. In case of sweetened condensed milk, the keeping quality is increased as the sugar prevents the growth of micro-organisms by increasing the osmotic pressure (osmoanabiosis) whereas in the unsweetened condensed milk, it is by plasmolysis. Condensed milk can be diluted for use as fresh milk.

Memory Effect & Battery Performance:

138 Guidance for Children Memory Effect & Battery Performance Memory effect is a term used to describe a self-conditioning phenomenon by which nickel-cadmium cells tend to adjust their electrical properties to a certain duty cycle to which they have subjected fro extended period of time. Temporary loss in capacity is due to: Large number of unvarying partial discharge charge cycles. Extended storage without recharge or to extended periods with insufficient charge. Prolonged constant current charging. Temporary loss in capacity means that the cells fails to deliver power if an attempt is made to discharge them beyond the lower limit of the repetitive discharge cycle. Complete discharge followed by recharge at not-too-low currents can eliminate this effect. Another reason for temporary loss in capacity, and often confused with memory effect, has to do with the formation of alloys of nickel and cadmium under conditions of high temperature overcharge.

Finger Nails and Toe Nails:

139 Guidance for Children Finger Nails and Toe Nails Fingernails are made up primarily of dead cells, a horn-like material called keratin. Growth takes place in the matrix, the hidden part of the nail under the cuticle (the tissue that overlaps with the visible part of the nail and rims the base of the nail). The older cells die and harden as they are pushed out. The matrix also includes the lunula, the whitish half-moon area at the base of the nail. Fingernails grow about 0.1mm per day or 36mm a year, and toenails grow at about 14mm a year. Finger nails and toe nails differ in growth. Possible reasons: Fingers nails are used more often and thus prone to injury and the body needs to replenish any damaged nails fast. Nails grow faster when temperature is higher. Fingers are constantly exposed but toe nails are mostly covered with shoes or slippers. Also, they are more damp.

Walking on Burning Coal:

140 Guidance for Children Walking on Burning Coal People wet their feet abundantly before walking on burning coal. When they start walking on the coal, this moisture (may also be due to sweat) evaporates and forms a protective gaseous layer beneath their feet. They walk on a protective layer of water vapour (which has low heat capacity and poor thermal conduction) rather than on the burning coal, as one would believe. This is a short time effect and one should walk quickly to avoid any further damage. Coal or wood embers, on which people generally walk, have low heat capacity and poor thermal conduction. It means coal being a bad conductor of heat will not pass heat as efficiently as metals.

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