Vidyamandir Classes Light, Shadows & Reflections

Light, Shadows & Reflections

BASIC

Introduction
Light is a form of energy that gives us a sensation of sight.
How do we see things?
We can see thing (objects) when light is given off from or reflected by an object.
We cannot see a book in a dark room becasuse there is not source of light in that room.

Luminous and Non-Luminous Objects

Luminous Objects that emit light of their own are called luminous objects. Sun, fire flies, fire, candle end electric bulb
are luminous objects.

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Non-luminous Objects: Those bodies which do not emit light but are made visible by light falling from some luminous
object on them, are Called non-luminous bodies, for example, the moon, the earth, a table, a chair etc

 An object that gives out light is called a luminous object.

Eg: Sun, candle, lamp, torch, diya, fireflies, lantern etc.
 An object that does not give out light is called non-luminous object.
Eg: paper, table, kite bell, bed , clock, buildings etc.

Transparent, Translucent, and Opaque Objects

Materials can be classified based on the amount of light they transmit. Materials, which allow complete transmission
of light, are called transparent. Any object can be seen through a transparent material. One example of transparent
material is pure glass. Opaque materials either reflect or absorb any incident light. As a result, light rays cannot pass
through opaque materials wood, stone, etc, are opaque materials. Translucent materials allow partial transmission of
light through them. A part of the incident light may get reflected or scattered, as it passes through the interior of the
material. Any object, seen through a translucent material, appears fuzzy of blurred. Some examples are oily paper,
tissue, some plastics, etc.

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If your are able to see clearly through an object, it is allowing light to pass through it and is transparent. For example:
water, clear glass etc.
If we cannot see through an object at all, it is an opaque object. For example: wooden door, wall etc.
There are some objects through which we can see, but not very clearly. Such Objects are known as translucent.
For example: Butter paper, ground glass etc
S.NO VALUE POINT TRANSPARENT TRANSLUCENT OPAQUE
1. Allows light or not Allows light to pass Allow light to pass Does not allow light
through it completely. through it partially. to pass through it
2. We can see or We can see clearly We can see partially We cannot see
not through them. through them. through them.
3. Casting shadow do not cast shadow Make faint shadows Form shadow as they
as they don’t block light block the light.
Examples: glass Frosted glass, wall, table
butter paper, clouds

Shadow and its formation

If an opaque object comes in the path of light then a dark patch formed on the other side of the object is the shadow
of that object

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When light does not pass through opaque objects it forms SHADOW.

Source of light is very important for the formation of shadow. We cannot see our shadow in a completely dark room
or without any source of light
Shadows can only be formed on an opaque screen
A shadow is a dark area on a bright surface. A shadow is formed behind an object when it blocks the light
Light is always required for a shadow to form. Shadows can never form in total darkness.
Shadows does not give us accurate information about the shape or colour of the object.

Rectilinear Propagation
Light always travels in a straight path. This is called rectilinear propagation of light.
• Light travels in a straight line (rectilinear propagation)
• Rectilinear propagation of light is responsible for the forming of shadows-light cannot travel around an
object.

Pinhole Camera

• It is a simple camera without a lens and with a single small aperture

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• Light proof box with a small hole in one side

• Light from a scene passes through a single point ad projects an inverted image on the opposite side of the
box

How does a Pinhole Camera Work?

A pinhole camera is a light-proof box. Light enters the box through a tiny pinhole on one side and strikes the opposite
wall of the box, where light-- sensitive paper or film (or even a CCD) records an image. The recorded image is upside
down (as in all cameras) and focused because the light rays- which travel in straight lines- do not cross each other
inside the box.

Steps for Making Pinhole

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We should never observe sun directly because it can cause severe damage to our eyes. But we can use a pinhole
camera to observe sun and its various images during an eclipse. The image of sun can be clearly visible on the screen
in a pinhole camera.
Natural pinhole camera can be seen in everyday life. If we pass under a tree covered with large number of leaves, we
see bright patches of light on the ground. These are the pinhole images of the sun. In this case the sun is the object,
the gap between the leaves are the pinholes and the ground acts as a screen.

Characteristic of images formed by a pin hole camera.

The image formed by pinhole camera are:
(i) They are inverted in nature
(ii) Images are always smaller in size in comparison to the object
(iii) They can be obtained on the screen

Reflection of Light
Reflection is when light bounces off on object. If the surface is smooth and shiny. Like glass, water or polished
metal, the light will reflect at the same angle as it hit the surface. This is called specular reflection.

Diffuse reflection is when light hits an object and reflects in lots of different directions. This happens when the
surface is rough. Most of the things we see are becasuse light form a source has reflected off it.
The angle at which light hits a reflecting surface is called the angle of incidence and the angle at which light bounces
off a reflecting surface is called the angle of reflection
If your want to measure these angles, imagine a perfectly straight line at a right angle to the reflective surface
(this imaginary line is called normal’). If you measure the angle of incidence and the angle of reflection against the
normal the angle of incidence is excatly the same as the angle of reflection. With a flat mirror, it is easy to show that
the angle of reflection is the same as the angle of incidence.

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Water is also a reflective surface. When the water in a lake or sea is very still, the reflection of the landscape is perfect,
becasuse the reflecting surface is very flat. However, if there are ripples or waves in the water, the reflection becomes
distorted. This is because the reflecting surface is no longer flat and may have humps and troughs causes by the
wind.
It is possible to make mirrors that behave like humps or troughs and because of the different way they reflect light,
they can be very useful.
Numerical. if angle of incidence (with the normal) is 60 degree, find angle of reflection. The angle of reflection is also
60 degrees (with the normal), as angle 1 = angle r
Mirrors are opaque objects. It is actually a thin glass slab with its one side coated with silver (or aluminium). The silver
coating is protected by a red paint. The silver coating makes the plane mirror shiny.
A plane mirror is a mirror with a flat (planar) reflective surface. For light rays striking a plane mirror, the angle of
reflection equals the angle of incidence. The angle of the incidence is the angle between the incident ray and the
surface normal (an imaginary line perpendicular to the surface).
normal
angle of angle of
incidence reflection reflected ray
incident ray
i=r
i r

mirror

Difference between image and shadow

Image:
1. It is formed by intersection of reflected rays.
2. Image is seen when reflected rays approach to observer’s eyes
3. Image gives more information such as colour, structure etc.
4. Image can be straight or inverted

Shadow:
1. Shadow is formed when light does not reach behind the object.
2. No light enters the observer’s eyes.
3. Shadow does not provide such information
4. Shadow is never inverted.

What is an eclipse?
An eclipse is formed when one object in space blocks an observer from seeing another object in space. There are two
main types of eclipses: solar esclipse and lunar eclipse.

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In a solar eclipse, the moon passes between earth and the sun and stops some or all of the Sun’s light from reaching
Earth. There are three kinds of solar eclipses. In a partial solar eclipse, the Sun is partly covered when the Moon
passes in front of it. In a total solar eclipse, the Moon completely covers the Sun. In an annular solar eclipse, the
Moon does not completely cover the Sun but leaves the edge of the Sun showing. This last type of eclipse happens
when the Moon is farthest in its orbit from Earth and Earth is closest in its orbit to the Sun, which makes the Moon’s
disk too small to cover the Sun’s disk completely.

During a lunar eclipse, Earth gets in the way of the sun is light hitting the moon. That means that during the night,
a full moon fades away as Earth’s shadow covers it up.

Good to know for our little astronomers

The umbra is the region of a shadow from which the light source is completely obscured by the object
The umbra is the region of shadow from which the light source is completely obscured by the object casting the
shadow. It is the darkest part of the shadow.
The penumbra is the region from which the light source is only partially obscured. If you are in the penumbra, you can
still see part of the light source.

When it comes to eclipses, the light source is the Sun. So if you witness a total solar eclipse, then you are in the
Moon’s umbra - the Sun is completely obscured.

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If you witness a partial solar eclipse, you are in the penumbra - you can still see part of the Sun.
If the witness a total lunar eclipse, then the Moon is completely inside Earth’s umbra-no part of the Sun is visible from
the face of the Moon.

If you witness a partial lunar eclipse, then only part of the Moon is in Earth’s umbra; the rest of the Moon’s surface
is in Earth’s penumbra.

SOME INTERESTING FACTS

It takes 8 minutes 17 seconds for light to travel from the Sun’s surface to the Earth
When sunlight is intercepted by a drop of water in the atmosphere, some of the light refracts into the drop, reflects
from the drop’s inner surface, and then refracts out of the drop. The first refraction separates the sunlight into its
component colour, and the second refraction increases the separation. The result is rainbow.
The bending of light as it passes from one transparent substance to another, like air to water, is called refraction.

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SOLVED EXAMPLES
Multiple Choice Questions:
1. A smooth shining surface, which rebounds the light back in same or in different direction, is called
(a) a mirror (b) a lens
(c) reflection of light (d) point of incidence
Ans.(a)
2. Beam of light striking the reflecting surface is called
(a) reflected ray (b) incident ray
(c) refracted ray (d) normal ray
Ans.(a)
3. Band of seven colours is called
(a) VIBGYOR (b) spectrum
(c) dispersion (d) reflection
Ans.(b)
4. Which of the folloiwng characteristics is not exhibited by the shadow of an object?
(a) Right side up (b) same color as object
(c) Can be formed on a screen (d) can be bigger than the object
Ans.(b)
5. Read the folloiwng sentences carefully, and choose the correct one
(a) An object which reflects light very well is called a mirror.
(b) A plane mirror is a thin, flat and smooth sheet of glass having a shiny cooting of silver metal (or minimum metal) on
one side.
(c) It is due to the irregular reflection of light produced by the rough surface of piece of white paper that we cannot see
the image of our face on looking into the piece of paper.
(d) All the above
Ans.(d)
6. Which of the folloiwng statement is or are incorrect?
(a) A narrow beam of light is called a ray.
(b) The process of sending back the light rays which tall on the surface of an ojbect, is called reflection of light
(c) The objects having polished, shining surfaces reflect more light than objects having unpolished, dull surfaces.
(d) None of the above
Ans.(d)
7. In a quiz competition, you are asked a question where you have to choose the statement which is/are correct?
(a) The pinhole camera works on the principal that light travels is in straight-cross lines
(b) An erect image is formed in a pinhole camera very simply.
(c) A pinhole camera forms a real and inverted image of an object.
(d) The pinhole camera is a complex device to see the images of various objects.
Ans.(c)

Subjective Questions
8. Give two examples of luminous objects.
Ans. Sun, Bulb, etc

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9. What is the difference between light emitted by the moon and the sun?
Ans. The sun is a luminous body which emits its own light whereas moon reflects the sunlight falling on it.
10. Give one exaple of an artifical soruce of light.
Ans. Bulb, Torch etc.
11. Wrtie the characteristics of an image formed by a pinhole camera.
Ans. The image formed by a pinhole camera is real and inverted.

EXERCISE BASED ON CBSE

Multiple Choice Questions:

1. Which of the following is/are not always necessary to observe a shadow?
(A) Sun (B) Screen (C) Source of light (D) Opaque object

2. Paheli observed the shadow of a tree at 800 am, 1200 noon and 3.00 pm which of the following statments is closest to
her observation about the shape and size of the shadow?
(A) The shape of the shadow of the tree changes but the size remains the same
(B) The size of the shadow of the tree changes but the shape remains the same.
(C) Both the size and shape of the shadow of the tree changes.
(D) neither the shape nor the size of the shadow changes.

3. Which of the following can never form a circular shadow?

(A) A ball (B) A flat disc (C) A shoebox (D) An ice cream cone

4. Two students while sitting across a table looked down on to its top surface. They noticed that they could see their own and
each others image. The table top is likely to be made of
(A) unpolished wood (B) red stone
(C) glass sheet (D) wood top covered with cloth

Subjective Questions
5. Is air around use always transparent? Discuss.
6. What is a natural pinhole Camera? Discuss.
7. A student coved a torch with red cellophane sheet to obtain red light. using the red light, she obtains a shadow of an
opaque object. She repeats this activity with green and blue lights. Will the colour of the light affect the shadow? Explain.
8. A foot ball match being played at night in stadium with flood lights on. You can see the shadow of a football kept at the
ground but cannot see its shadow when it is kicked high in the air. Explain.
9. What is a shadow? How is it formed? How does the colour of an opaque object affect the colour of the shadow?
10. Explain ‘‘Real Images’’ and ‘’virtual images’’.

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NSO EXERCISE

1. The shape of the shadow does not depend upon ______.

(a) The shape of the object (b) The position of the source of light
(c) The size of the object (d) The size of the source of light

2. A translucent object allows light to _________.

(a) Transmit completely (b) Transmit partially
(c) Bounce back completely (d) None of these

3. Manu placed three different types of materials I, II and III in front of letters P, Q and R as shown in the figure and
tried to look from the other side of each. Which of the following is correct?
(a) Material II is frosted glass (b) Material I is glass window.
(c) Material III is wooden door (d) All of these

4. Which of the following statements is correct?

(a) Eclipse occurs due to reflection of light
(b) A person located in umbra region may not see the source of light directly
(c) Moon is a luminous body
(d) The size of the shadow depends on the size of object only

5. A lunar eclipse occurs

(a) When the earth conies between the sun and the moon
(b) When shadow of the moon falls on the earth
(c) When the moon is waxing
(d) On any night

6. Which of the following properties is/are correct about the image formed by a plane mirror?
I. The image is at the same distance from the mirror as the object
II. The image is upside down.
III. The image is laterally inverted.
(a) I only (b) I and III only (c) II and III only (d) I, II, and III

7. Which of the following statements is/are incorrect?

(i) The size of a shadow changes with the distance between the light source and the object.
(ii) The dark part of a shadow that receives no light from the source is called the penumbra.
(iii) The image formed by a pinhole camera is always of the same size as the object.
(iv) During solar eclipse the shadow of the moon falls on the Earth.
(a) (i) and (ii) only (b) (iii) and (iv) only (c) (i) and (iv) only (d) (ii) and (iii) only

8. Read the given paragraph with few blanks and select the option that correctly fills these blanks. An eclipse
occurs when a planet or moon gets in the way of the sun's light. If the moon is completely hidden by the shadow of
the earth, it is called (i). In solar eclipse the (ii) casts a shadow on the (iii). Lunar eclipse occurs at (iv) and solar
eclipse occurs only at (v) day.
(i) (ii) (iii) (iv) (v)
(a) Total lunar Moon Earth New moon Full moon
(b) Total solar ecipse Sun Moon Full mon New moon

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(c) Total solar eclipse Earth Moon New moon Full moon
(d) Total lunar eclipse Moon Earth Full moon New moon

9. Read the given statements and select the correct option.

Statement 1: At sunrise or at sunset, the shadows on the ground become much longer than the sizes of the objects.
Statement 2. The size of the shadow becomes smaller when the object is brought near the light source or the screen
is moved away from the object
(a) Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1
(b) Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1
(c) Statement 1 is true but statement 2 is false
(d) Statement I is false but statement 2 is true

10. A solid transparent sphere has a small opaque dot at its centre. When observed from outside, the apparent position
of the dot will be
(a) Closer to the eye than its actual position
(b) The same as its actual position
(c) Farther away from the eye than its actual position
(d) None of these

11. Which of the following statements are correct?

(i) The shape of a shadow depends on the position of the source of light.
(ii) A plane mirror can change the direction of light falling on it.
(iii) A pinhole camera forms an erect image of an object on a screen.
(iv) A shadow is formed when light passes through a transparent object.
(a) (i) and (iii) only (b) (ii) and (iv) only
(c) (i), (ii) and (iii) only (d) (i) and (ii) only

12. Which of the following statements about pinhole camera are correct?
(i) It is a camera with a single lens (ii) It produces an upside down image of object
(iii) It does not have a screen (iv) It works because light travels in a straight line
(v) It forms real and colourless shadows of objects
(a) (i) and (v) only (b) (ii) and (iv) only (c) (i), (iii) and (iv) only (d) (ii), (iv) and (v) only

13. A plane mirror reflect a pencil of light to form a real image. Then the pencil of light incident on the mirror is
(a) Parallel (b) Convergent (c) Divergent (d) None of these

14. Vijay puts some water into four cups made of steel, Porcelain, glass frosted glass respectively. Which one of these
cups will allow him to see the level of the water clearly.
(a) Glass cup (b) Steel up (c) Porcelain cup (d) Frosted glass cup

15. A solid transparent sphere has a small opaque dot at its centre. When observed from outside, the apparent position
of the dot will be
(a) Closer to the eye than its actual position (b) The same as its actual position.
(c) Farther away from the eye than its actual position (d) None of these

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SOLUTIONS TO EXERCISE BASED ON CBSE

Multiple Choice Answers

1.(A) Sun is source of light any source light can replace it so sun is not always necessary to observe a shadow
2.(C) Sun is source of light there and it changes its position at different points of time. So according size and shape of the shadow
of the tree change
3.(C)
4.(C) Out of the given options, only glass sheet can reflect light properly in order to form their images

Subjective Answers
5. We can see the objects through air clearly, means we can observe all the objects in their original shapes and sizes without
any disturbance. It means the environment around us which is just air, must be transparent. But when thick smoke thick
clouds etc. are presents in the air, it does not remain transparent.
6. There is an interesting pin hole camera in nature. Sometimes. when we pass under a tree covered with large number of
leaves, we notice small patches of sun light under it. These circular images are in fact. pin hole images of the sun. The gaps
between the leaves, act as the pin holes. These gaps are all kinds of irregular shapes but. we can see circular images of the
sun.
7. Shadow is just an absence of light at that place. Shadow is not affected by the colours of the object because the amount of
light preventing to pass will remain same.
The shadow is affected by the size of the object only. If the object is large, the shadow will be large and vice-versa
8. The shadow of an object cannot be caught if the screen and the object are very far from the each other. This is the same case.
Here, also the shadow of the football cannot be seen on the ground (which acts as a screen) when it is kicked high in the air.
This happens because it we take the object away from the screen, the shadow becomes smaller and smaller in size and a time
comes when it totally disappears from the screen.
9. A shadow is a dark outline or image cast by an opaque object that blocks light coming from a source of light. It is formed
when light hits the opaque object which does not let the light pass through. Everywhere else around the opaque object, the
light continues in a straight path until it bounces of the ground or wall behind the object. The wall or ground behind the
opaque object is the screen. On this screen is a dark patch, or shadow, with the same outline as the object surrounded by
light. The colour of the opaque object does not affect the colour of the shadow that is formed.
10. The image which can be obtained on a screen is called a real image. The image formed on a cinema screen is an example of
real images. A real image is formed when light rays coming form an object actually meet at a point after reflection form the
mirror. A real image is formed when light rays coming from an object actually meet at a point after reflection from the mirror.
A real image can be formed on a screen because light rays actually pass through it.

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SOLUTIONS TO NSO EXERCISE

Multiple Choice Answers

1.(c) Shape of the shadow does not depend upon the size of the object.
2.(b) A translucent object allows light to transmit partially not enough to see clearly through it.
3.(b) As letter P is clearly visible, material I is transparent i.e., glass window.
As letter is not visible at all, material II is opaque is, wooden door As letter R is partially visible, material III is
translucent is frosted glass.
4.(b) The umbra region is the innermost add darkest part of a shadow, where light source is completely blocked by occluding
body
5.(a) A lunar eclipse occurs when the earth comes between the Sun and the Moon.
6.(b) The image formed by a plane mirror is always erect.
7.(d) The dark part of a shadow that receives no light from the source is called the umbra. The image formed by a pinhole
camera is always of the smaller size than the object,
8.(d) (i) Total lunar eclipse; (ii) Moon; (iii) Earth; (iv) - Full Moon; (v) - New moon.
9.(c) The size of the shadow become larger when object is brought near the light source or the screen moved closer to
the object.
10.(b) The position will remain same
11.(d) A pinhole camera forms a real and inverted image of an object on a screen. A shadow is formed when light does
not pass through any object. The path of light is obstructed by opaque objects.
12.(b) A pinhole camera is a simple camera without a lens but with a tiny aperture. A pinhole effectively a light proof box
with a small hole ide. Light from a scene passes through the aperture and projects an opposite side of the box.
The image of a pinhole came onto a translucent screen for real time viewing.
13.(b) A plane mirror can form a real image if the object itself is virtual. That is possible with a convergent beam of light.
14.(a) A glass is a transparent material. It allows light to pass through it.
15.(b)

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LIGHT, SHADOWS AND REFLECTIONS

Concept Map

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