CB01.10.PHYS.PPT.04 05

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Slide 1: 

CLASS X Chapter 3- Electricity

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CURRENT ELECTRICITY

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series Parallel Electricity Introduction Electric current Electric Energy And Power Combination Of Resistors Ohm's Law Circuit Diagram Electric Potential

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Direction Of Electronic Current -ve to +ve terminal Direction Of Conventional Current +ve to–ve terminal The rate of flow of charge across any cross-section of a conductor is known as electric current. It is a scalar quantity. I=Q/t 1 Ampere=1 Coulomb/ 1 second Electric Current

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When 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the electric current flowing through it is said to be 1 ampere.

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Current is measured by an instrument called ammeter. An ammeter should have very low resistance.

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The electrostatic potential at any point is defined as the work done in bringing a unit positive charge form infinity to that point. Symbol  V, S.I. Unit  volt +q0 At infinity +q0 Given point Electrostatic Potential

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The potential difference between two points in an electric field is defined as the amount of work done in moving a unit positive charge from one point to another point. +q0 +q0 Point A Point B Potential Difference

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It is a scalar quantity. It is measured by voltmeter and potentiometer.

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At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. I  V (at constant temperature) V=IR Ohm’s Law

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Electron CIRCUIT DIAGRAM

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The property of a conductor due to which it opposes the flow of current through it is called resistance. RESISTANCE Conductance: The inverse of resistance is known as conductance of the conductor. G=1/R ; S.I. unit of conductance is mho or (ohm) -1

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R of a conductor depends on : The nature of the material of the conductor; length of the conductor; area of cross section of the conductor; temperature of the conductor. Factors effecting Resistance

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It is a property of the material. It is numerically equal to the resistance of a rod of that substance which is 1 meter long and 1square meter in cross section. S.I. Unit of is ohm. m RESISTIVITY For metals and alloys of metals, the resistivity increases with rise in temperature.

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Hi! Can you tell me what will happen to the resistance of this wire whose resistance is 446.5 ohm, if I stretch it by one-tenth of its original length. I am giving you four options: (a) 50  (b) 54  (c) 12 (c) 20  LET’S TRY THIS New resistance=? R=446.5 ohm.

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As volume of the wire is constant. Thus new length of wire become: Let the new resistance be R2. Then

Combination of resistances : 

Combination of resistances Resistances In Parallel Resistances In Series

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The combined resistance of any number of resistances connected in series is equal to the sum of the individual resistance. R R Resistances In Series =

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Let R1, R2, R3 are three resistances connected in series with the battery of pd. V. Here

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= R/2 Resistances In Parallel

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The reciprocal of the combined resistance of a number of resistances connected in parallel is equal to the sum of the reciprocals of all the individual resistances. Resistances In Parallel Let R1, R2, R3 are three resistances connected in parallel with the battery of pd. V.

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Here

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I have a wire of resistance 10  , if i bent it to form a complete circle. Can you help me in finding the resistance between two diametrically opposite points say A and C.

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Soln. Let ABCDA be the wire of resistance 10 . We have to calculate the resistance of this loop between the diametrically opposite points A and C. The wires ADC and ABC will have resistances 5  each. These two are joined in parallel between A and C. The equivalent resistance R between A and C is, therefore, given by

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Electrical Energy Electric energy is the potential energy associated with the conservative Coulomb forces between charged particles contained within a system. Energy = Work done

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The Rate at which electrical energy is consumed is known as Electric power. S.I. Unit of power is watt. Electric power

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When an electric current is passed through a high resistance wire , the resistance wire becomes very hot and produces heat. This is called the heating effect of current. Factors on which heat produced are Heating Effects Of Current

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It is utilized in the electrical heating appliances such as electric iron, room heaters, water heaters etc. It is utilized in electrical bulbs for producing light. An ‘electric fuse’ is an important application of the heating effect of current. Practical Applications

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Symbols Terms Unit formula Q  Electrical charge Coulomb. Q = I x t V  Potential difference Volt V = IR I  Electrical current ampere  Resistivity Ohm – m t  Time Sec.(s) H  Heat Energy Joule.(J) H = I2Rt E Electrical energy Kilo watt hour E = P x t Glossary

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R  Resistance Ohm () R = V/I Rs Resistance in Series Ohm () Rs = R1 + R2 +……. Rp  Resistance in parallel Ohm () P  Power  Ammeter (measures current)  Voltmeter (measures potential difference)  Galvanometer (Sensitive to current also gives the direction of current) Resistance (fixed) Rheostat (Variable resistor)

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Or ( )  Closed key Or ( )  open key  Cell  Battery  Connecting wire  Wire joint  Wires crossing without contact  Electric bulb