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LIGHT,SHADOWS AND REFLECTION,PROPERTIES OF MIRRORS AND LENSES:

LIGHT,SHADOWS AND REFLECTION,PROPERTIES OF MIRRORS AND LENSES Sameer D. Devidas

CONTENTS:-:

CONTENTS:- LIGHT PROPERTIES OF LIGHT REFLECTION LAWS OF REFLECTION SHADOWS MIRRORS TYPES OF IMAGES TYPES OF MIRRORS IMAGE FORMATION BY MIRRORS LENSES TYPES OF LENSES AND IMAGE FORMATION

LIGHT AND LAW OF REFLECTION:

LIGHT AND LAW OF REFLECTION .

Light:

Light Properties of light Reflection

Part 1 – Properties of Light:

Part 1 – Properties of Light Light travels in straight lines: Laser

Slide6:

Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

Slide7:

Light travels much faster than sound. For example: Thunder and lightning start at the same time, but we will see the lightning first. 2 ) When a starting pistol is fired we see the smoke first and then hear the bang.

Slide8:

We see things because they reflect light into our eyes: Homework

Slide9:

Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objects Non luminous object - The Sun - Lamps - Lights - Lasers The Moon Mirrors People Objects

Properties of Light summary:

Properties of Light summary Light travels in straight lines Light travels much faster than sound We see things because they reflect light into our eyes

Part 2. The law of reflection:

Part 2. The law of reflection 1) Angle of incidence is always equal to angle of reflection. 2) The incident ray, reflected ray and Normal lies in a same plane.

Law of Reflection:

Law of Reflection Reflection from a plane mirror : Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

Law of Reflection:

Law of Reflection Some terms : 1) The ray of light which falls on the mirror surface is called incident ray. 2) The point at which the incident ray strikes the mirror is called the point of incidence. 3) The ray of light which is sent back by the mirror is called the reflected ray . 4) The ‘ normal ’ is a line drawn at right angles to the mirror surface at the point of incidence . 5) The angle between incident ray and normal is called the angle of incidence. The angle between reflected ray and normal is called the angle of reflection

Slide14:

Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at THE SAME ANGLE it hits it. q i q r q i = q r

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. Using the law of reflection, we can determine the location of images formed by plane mirrors.

Smooth v/s Diffuse Reflection:

Smooth v/s Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

SHADOW:

SHADOW

Formation of Shadow:

Formation of Shadow Three things required : A source of light An opaque object A screen or surface behind the object A shadow is formed when an opaque object blocks the light falling on it. The area of darkness formed behind the opaque object is called the shadow of the object.

Characteristics of Shadow :

Characteristics of Shadow Always black in colour Shape or outline of the object not the details Size varies depending on the distance between the object and the source of light, and the distance between the object and the screen

Slide20:

The shadow becomes bigger when the object is moved closer to the light source. The shadow becomes smaller when the object is moved closer to the screen. The shape of the shadow depends on the position of the object and the position of the source of light. Opaque objects dark shadow Translucent object faint shadow Transparent object no shadow

Difference between image and shadow:

Difference between image and shadow image shadow Has the colour of the object Gives the details as well as the outline of the object Undergoes lateral inversion Is always black Gives only the outline of the object Does not undergo lateral inversion

Umbra and Penumbra:

Umbra and Penumbra When the source is very small (point source) then a sharp well defined image is formed on the screen. This shadow is completely dark and is called umbra

Slide23:

When the source is wide (extended) two shadows are formed. One shadow is completely dark. It appears at the centre and is called the umbra. The other is a partial shadow called penumbra. Penumbra surrounds the umbra

Eclipses:

Eclipses Eclipses are shadows formed in space. Earth and the moon are the opaque objects . Sun is the source of light. Earth and the moon casts their shadows and cause eclipses. Two kinds of eclipses depending on the position of the sun, the moon and earth. 1) Solar eclipse 2) Lunar eclipse

Solar Eclipse:

Solar Eclipse Occurs when the moon comes between the sun and earth and when all three are in the same straight line, the shadow of the moon falls on earth.

Lunar eclipse:

Lunar eclipse Occurs when the earth comes between the sun and the moon and all three are in the same straight line, the shadow of the earth falls on the moon.

Shadowless Lighting:

Shadowless Lighting When the source of light is much larger than the object , the umbra is formed very close to the object. Thus by reducing the umbra region of the shadow a shadowless effect is produced. Birds and aircrafts fly too high for their umbra of their shadow to fall on the ground. The penumbra is very large and too faint to be seen. Shadows are formed when they fly closer to the ground

Daytime variation of the shadow:

Daytime variation of the shadow The shadow is constantly changing during the daylight hours. The angle of the sun with respect to the horizon determines the length of the shadow during the day. At sunrise and sunset when the sun is near the horizon shadows are the longest. At noon when the sun is overhead shadows are the shortest.

Slide29:

It is the rotation of the earth and the apparent motion of the sun that causes the shadows to change during the day. The pattern is that the shadow grow shorter from sunrise to noon and longer from noon to sunset. The 2 nd pattern is that the shadow moves from the west through the north to the east as daylight progresses from sunrise to sunset.

MIRRORS :

MIRRORS

Sub-Topics:

Sub-Topics Types of images Plane mirrors Concave mirrors Convex mirrors Image formation by Spherical mirrors

Slide32:

Real Image – Image is made from “real” light rays that converge at a real focal point so the image is REAL Can be projected onto a screen because light actually passes through the point where the image appears Always inverted

Real Image:

Real Image Real Images are ones you can project on to a screen. For MIRRORS they always appear on the SAME SIDE of the mirror as the object . object image The characteristics of the image, however, may be different from the original object. These characteristics are: SIZE ( reduced,enlarged,same size) POSITION (same side, opposite side) ORIENTATION (right side up, inverted)

Slide34:

Virtual Image – “Not Real” because it cannot be projected Image only seems to be there!

Virtual Images:

Virtual Images Virtual Images are basically images which cannot be visually projected on a screen. If this box gave off light, we could project an image of this box on to a screen provided the screen was on the SAME SIDE as the box. You would not be able to project the image of the vase or your face in a mirror on a screen, therefore it is a virtual image. CONCLUSION: VIRTUAL IMAGES are ALWAYS on the OPPOSITE side of the mirror relative to the object.

Plane Mirrors:

Plane Mirrors Plane mirrors are a flat sheet of glass, that has a silver-colored coating on one side the coating reflects the light The coating is smooth = regular reflection occurs and a clear image forms Image is a copy of an object formed by reflected or refracted rays of light

Virtual Images in Plane Mirrors:

Virtual Images in Plane Mirrors     If light energy doesn't flow from the image, the image is "virtual". Rays seem to come from behind the mirror, but, of course, they don't.  It is virtually as if the rays were coming from behind the mirror. "Virtually":  the same as if As far as the eye-brain system is concerned, the effect is the same as would occur if the mirror were absent and the chess piece were actually located at the spot labeled "virtual image".                                     

LEFT- RIGHT REVERSAL:

LEFT- RIGHT REVERSAL AMBULANCE

Spherical Mirrors – Concave & Convex:

Spherical Mirrors – Concave & Convex Also called CONVERGING mirror Also called DIVERGING mirror

Concave Mirrors:

Concave Mirrors Curves inward May be real or virtual image View kacleaveland's map Taken in a place with no name (See more photos or videos here ) "Have you ever approached a giant concave mirror? See your upside-down image suspended in mid-air. Walk through the image to see a new reflection, right-side-up and greatly magnified. In the background you see reflected a room full of visitors enjoying other

Converging (Concave) Mirror:

Converging (Concave) Mirror Since the mirror is spherical it technically has a CENTER OF CURVATURE, C . The focal point happens to be HALF this distance. We also draw a line through the center of the mirror and call it the PRINCIPAL AXIS OR OPTICAL AXIS.

For a real object between f and the mirror, a virtual image is formed behind the mirror. The image is upright and larger than the object. :

For a real object between f and the mirror, a virtual image is formed behind the mirror. The image is upright and larger than the object. For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.

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For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object. For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.

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For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object. For a real object at C, the real image is formed at C. The image is inverted and the same size as the object. For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.

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For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object. For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.

:

For a real object at f, no image is formed. The reflected rays are parallel and never converge. For a real object at f, no image is formed. The reflected rays are parallel and never converge. What size image is formed if the real object is placed at the focal point f?

Convex Mirrors:

Convex Mirrors Convex Mirrors are mirrors with surfaces that curve outwards rays spread out but appear to come to from a focal point behind the mirror Because rays never meet, images formed by convex mirrors are always virtual and smaller than the object Used in car mirrors Advantage: allows you to see a larger area than you can with a plane mirror Disadvantage: images appears further away than it really is

LENSES:

LENSES

Slide49:

Lens A lens is a piece of transparent material in which light is able to pass through and is used to refract light.

LENS:

LENS A lens is a device that bends light. A lens is a piece of transparent material. If it is transparent, you can see through it. It is usually made of glass and has at least one curved surface.

Lenses and Images:

Lenses and Images A lens forms an image by REFRACTING light rays that pass through it. The type of image formed by a lens depends on the shape of the lens and the position of the object.

TWO TYPES OF LENSES:

TWO TYPES OF LENSES There are 2 types of lenses: CONVEX CONCAVE

Slide53:

The converging lens causes horizontal light rays to converge (come together) when it hits. The diverging lens causes horizontal light to diverge (move apart) when it hits.

Slide54:

It looks like there is a cave on both sides!! So, it must be con cave !! Concave Lens A concave lens is thinner in the middle than at the edges and causes light rays to spread apart (divergence)

Slide55:

2f f 2f f Ray Diagrams (for concave (DIVERGING) lenses) The first light ray we draw goes through the center of the lens This light ray passes through unaffected and keeps going the same way

Slide56:

2f f 2f f Ray Diagrams (for concave lenses) The second light ray we draw goes horizontally towards the lens and stops in the center of it This light bends as if it came from the focal point on the front of the lens

Slide57:

2f f 2f f Ray Diagrams (for concave lenses) The last light ray we draw goes TOWARDS the focal point on the other side and stops at the center of the lens This light ray bends and emerges horizontal on the back side

Slide58:

Describe the image: Virtual Upright Smaller 2f f 2f f A concave lens (diverging) with (f = 2 cm, d 0 =5 cm) Putting it all together. Draw all three rays and extend the refracted rays back behind the lens. The point where the extensions meet is the image point Rays don’t intersect over here so they are extended back to the front of the lens Image

Concave Lenses and Images:

Concave Lenses and Images A concave lens produce upright images that are smaller than the real object.

Concave lens:

Concave lens

Convex Lens:

Convex Lens A convex lens or magnifying glass is thicker in the middle then on the ends which causes the light rays focus (converge)

Slide62:

2f f 2f f Ray Diagrams (for convex lenses) The first light ray we draw goes through the center of the lens This light ray passes through unaffected and keeps going the same way

Slide63:

2f f 2f f Ray Diagrams (for convex lenses) The second light ray we draw goes horizontally towards the lens and stops in the center of it (the light actually bends the whole time its in the lens, but as a convention we make it bend when it hits the center. This light bends and passes through the focal point on the other side of the lens

Slide64:

2f f 2f f Ray Diagrams (for convex (CONVERGING) lenses) The last light ray we draw goes through the focal point on the front side at stops at the center of the lens This light ray bends and emerges horizontal on the back side

Slide65:

image Describe the image: Real Inverted Smaller 2f f 2f f Putting it all together. Draw all three rays and the point where they intersect represents the point where the tip of the image will be formed

Slide66:

Describe the image: Virtual Upright Larger 2f f 2f f Special Examples (For Convex Lenses) 1- When the object is located exactly on (f) the rays will not intersect anywhere and there will be no image 2- When the object is placed in front of (f) the rules are a little bit different Notice the rays do not intersect on this side. So we have to extend these refracted rays back to the front of the lens to see where they appear to come from The first two rays are the same as before The third ray cannot be drawn through (f) since we are in front of it so it is drawn as if it originated at (f), and this ray refracts horizontal after hitting the center. Image

Slide67:

Convex Lens and images Depending on where you hold the lens--the image you see will either be right side up (real image) or upside down(virtual image)

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