NCERT Solutions Class 7 Science Chapter 11 Light Shadows and Reflections

F R E E S T U D Y M AT E R I A L F O R E V E R Y S T U D E N T

CLASS 7 · SCIENCE

NCERT Solutions

Chapter 11: Light: Shadows and
Reflections

NCERT Textbook — Curiosity

BOOK PAGES SECTIONS QUESTIONS MEDIUM

153 – 168 20 47 English

Solutions, notes, sample papers & more at 46 pages

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

CLASS 7 · SCIENCE · CURIOSITY

NCERT Solutions — Chapter 11: Light: Shadows and
Reflections
Complete NCERT Solutions for Class 7 Science Chapter 11 Light: Shadows and Reflections from the NCERT
textbook Curiosity. Every question is answered — Activities 11.1 to 11.10 with Tables 11.1 and 11.2 filled in,
both Dive Deeper boxes, every in-text question, all 12 questions of Let Us Enhance Our Learning and the
Exploratory Projects — with ray diagrams drawn for shadows, mirrors, the pinhole camera and the
periscope.

TEXTBOOK BOOK PAGES

Curiosity (Class 7) 153 – 168

SECTIONS QUESTIONS

20 47

MEDIUM

English

In-text Questions — Page 153
Chapter opening — Keshav wonders about moonlight

Q1 Does the Moon actually produce its own light? Is moonlight just reflected sunlight?

No, the Moon does not produce any light of its own. Moonlight is sunlight that the Moon
reflects towards us.
The Moon is a non-luminous object. Sunlight falls on the Moon's rocky surface, and a small part
of it bounces off and reaches the Earth. That is why we see the Moon shining at night.

Why it happens: Only a body that is very hot or is made to glow (like the Sun, a star
or a burning flame) can send out light of its own. The Moon is cold rock — it has no
way of making light, so it can only pass on the light it receives.

Did you know? The same is true of the planets. Mars and Venus look like bright
stars in the night sky, but they shine only by reflecting sunlight. You read this in the
chapter ‘Beyond Earth’ of the Grade 6 textbook Curiosity.

Page 1 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q2 Which objects give off their own light?

Objects that give off their own light are called luminous objects.

NATURAL SOURCES ARTIFICIAL (MAN-MADE) SOURCES

The Sun, the stars, lightning A burning candle, oil lamp, kerosene lamp

Natural fire, red-hot lava Electric bulb, tube light, LED lamp

Fireflies (glow-worms) and some deep-sea animals Torch, mobile phone screen, gas lamp

Everything else — the Moon, a mirror, a table, a book, Mars, Venus — is non-luminous. We see
these things only because light from a luminous object falls on them and comes to our eyes.

Activity 11.1: Let us investigate — Page 155
11.2 Does Light Travel in a Straight Line?

ACTIVITY

Q1 Move one of the matchboxes slightly to a side or up and down. Are you able to
obtain the light spot on the screen now?

No. The bright spot disappears from the screen the moment one of the three holes moves out
of the line.

Page 2 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

All three holes in one line — bright spot is seen

spot

Middle box lifted — no spot on the screen

no spot

Light from the torch reaches the screen only while the three holes lie along one straight line.

Why it happens: Light from the torch can only go straight. As long as the three
holes are on one straight line, that straight path is open and the light reaches the
screen. Shifting one box makes its hole step out of the path, the cardboard of that
box blocks the light, and the screen goes dark. Light cannot bend around the box to
find the next hole.

Check it yourself: Bring the box back into line very slowly. The spot reappears
exactly when the three holes and the torch bulb line up — nothing else about the
set-up has changed.

Q2 Can we somehow check it in some other way?

Yes. The straight-line travel of light can be checked in several simple ways:

Straight and bent pipe (Activity 11.2) — a candle flame is seen through a straight pipe but
vanishes as soon as the pipe is bent.
Laser beam in milky water (Dive Deeper, page 156) — the beam is seen as a perfectly
straight thread of light inside the beaker.
Shadows — an object always throws a shadow of its own outline right behind it, exactly
where a straight beam would be blocked.
Sunbeams — light entering a dark room through a small window, or through leaves in a
misty forest, is seen as straight beams.

Page 3 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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Try This: Look at a bulb through a rolled paper tube. Bend the tube even a little and

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Activity 11.2: Let us explore — Page 155
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11.2 Does Light Travel in a Straight Line?

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ACTIVITY
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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Straight pipe → flame visible

Bent pipe → flame not visible

Why it happens: Light from the flame travels only in straight lines. In the straight
pipe there is a clear straight path from the flame to your eye. When the pipe is bent,
that straight path meets the wall of the pipe. The light strikes the inside wall and is
stopped there, so nothing reaches your eye.

Tip: This is exactly why a periscope needs mirrors at its bends (Section 11.8.1). Light
will not turn a corner by itself — it has to be turned by a mirror.

Dive Deeper — Page 156
11.2 Does Light Travel in a Straight Line?

DIVE DEEPER

Q1 Pass a laser beam through a beaker filled with water in which a drop of milk is
added to make the laser beam easily visible. What do you observe? Do you see that
the beam of laser light inside water follows a straight path?

Inside the milky water the laser beam is seen as a thin, perfectly straight red line going from
one side of the beaker to the other. Yes — the beam follows a straight path in water too.

Why it happens: Plain water is transparent, so a beam passing through it cannot be
seen from the side. The tiny fat droplets of milk scatter a little of the light sideways
to your eye, and that scattered light traces out the path of the beam. What it traces
is a straight line — showing that light travels straight in water just as it does in air.

Caution: Use a low-power laser pointer only, under your teacher's supervision, and
never point it at anyone's eyes.

Did you know? Light can be made to bend around corners — inside the thin glass
fibres (optical fibres) that carry telephone and internet signals. You will learn how
this happens in higher classes.

Page 5 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

In-text Question — Page 156
11.3 Light through Transparent, Translucent, and Opaque Materials

Q1 What happens when an object comes in the path of light?

It depends on the material the object is made of:

MATERIAL OF THE WHAT HAPPENS TO THE WHAT YOU SEE ON THE SCREEN
OBJECT LIGHT

Transparent (clear glass) Passes almost completely Bright spot stays; a very faint shadow at
through most

Translucent (tracing paper) Passes partly through A dim, light shadow

Opaque (cardboard) Is completely blocked A dark shadow of the object's shape

Why it happens: Light moves in straight lines. If the material lets those straight rays
through, the screen stays lit. If the material stops them, the region of the screen just
behind the object gets no light at all — and that dark patch is the shadow.

Activity 11.3: Let us experiment — Pages 156 & 157

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

11.3 Light through Transparent, Translucent, and Opaque Materials

ACTIVITY

Q1 List the materials of the objects in Table 11.1 and classify them into transparent,
translucent, and opaque.
Table 11.1: Light through different materials

MATERIAL TRANSPARENT LIGHT WILL PASS FULLY / PARTIALLY / NOT AT
/ ALL
TRANSLUCENT
/
MY PREDICTION MY OBSERVATION
OPAQUE

Cardboard

Paper

Glass

Tracing
paper

Thick cloth

…

…

Here is Table 11.1 completed. The last two rows are objects you may add from your own
classroom.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

MATERIAL TRANSPARENT / LIGHT WILL PASS FULLY / PARTIALLY /
TRANSLUCENT / NOT AT ALL
OPAQUE
MY MY OBSERVATION
PREDICTION

Cardboard Opaque Not at all Not at all

Paper Translucent (thin paper) / Partially Partially — a dim glow is
Opaque (thick paper) seen through thin paper

Glass (clear window Transparent Fully Fully — the bright spot stays
glass) on the screen

Tracing paper Translucent Partially Partially — a blurred patch
of light

Thick cloth Opaque Not at all Not at all

Polythene sheet Transparent to translucent Fully Almost fully; slightly hazy
(thin, colourless)

Steel plate / wooden Opaque Not at all Not at all
scale

Tip: Judge a material by how clearly you can see through it — sharp view =
transparent, blurred glow = translucent, nothing at all = opaque.

Page 8 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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Tracing paper or thin cloth — the spot will still be there but dim and blurred.

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Cardboard, thick cloth or a steel plate — no, the spot will disappear and a dark patch (a
shadow) will take its place.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q3 Was your observation the same as your prediction? What conclusions could you
draw?

For most objects the observation matches the prediction. A surprise or two is normal — thin
paper often lets more light through than expected, and a coloured transparent sheet lets light
through but changes its colour.
The conclusions are:

Transparent materials → light passes almost completely

Translucent materials → light passes partially

Opaque materials → light does not pass at all

Why it happens: In a transparent material the light finds a clear straight way
through. In a translucent material the light is scattered again and again inside, so
only a part of it comes out and it comes out spread in all directions — which is why
the patch looks dim and blurred. In an opaque material the light is completely
absorbed or reflected at the surface, so none of it gets through.

In-text Questions — Page 157
11.4 Shadow Formation

Q1 What happens when an opaque object blocks the path of light?

The light is stopped, and a shadow is formed on the screen behind the object.
The shadow is simply the region of the screen that receives no light. Around it the screen stays
bright, because there the straight rays from the source arrive without hindrance.

Tip: A shadow always has the same outline as the object seen from the side of the
light source — never its colour and never its details.

Page 10 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q2 What did you see on the screen in Activity 11.3 when an opaque object was placed
in the path of light? Did you see a dark patch on the wall? Why was this dark patch
formed?

On the screen we saw a dark patch shaped like the object, surrounded by the lit part of the
screen. Yes, this dark patch was seen on the wall.
The dark patch was formed because light travels in a straight line. The opaque object stopped
every ray that was heading for that part of the wall. Since light cannot bend around the object to
fill in the gap, that part of the wall stayed dark — and a dark patch of this kind is called a
shadow.

Why it happens: Think of the rays as straight arrows shot from the torch. The
arrows that miss the object hit the wall and light it up; the arrows aimed at the
object are caught by it. The wall is dark exactly where the object's outline stands in
the way.

In-text Question — Page 158
11.4 Shadow Formation

Q1 Do translucent and transparent objects create shadows or not? Did you notice that
in Activity 11.3?

Yes, they do — but their shadows are much weaker than those of opaque objects.

TYPE OF KIND OF SHADOW EXAMPLE
OBJECT

Opaque Dark, sharp shadow Cardboard, a cricket ball, your own
body

Translucent Lighter, blurred shadow Tracing paper, butter paper, a thin
dupatta

Transparent A very faint shadow, sometimes with a bright A glass tumbler, a clear plastic scale
edge

Page 11 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: The darkness of a shadow depends on how much light is stopped.
An opaque object stops all of it, so the patch is fully dark. A translucent object lets a
part through, so that patch is only partly dark. A transparent object lets nearly all the
light through, yet its edges and curved surfaces still bend and reflect a little light —
that is why even a glass tumbler leaves a faint outline on the screen.

Activity 11.4: Let us explore — Page 158
11.4 Shadow Formation

ACTIVITY

Q1 Did the shadow form in all cases? Was the shape and size of the shadow the same as
the object? Record your observations in the second column of Table 11.2.
Table 11.2: Observation of shadows

ACTION OBSERVATIONS REGARDING
SHADOW

The screen is removed.

The object is removed.

The torch is switched off.

The object is moved closer to the screen, keeping the torch
and the screen fixed.

The object is moved closer to the torch, keeping the torch
and the screen fixed.

The object is tilted, keeping the torch and the screen fixed.

The colour of the object is changed.

No, a shadow was not formed in every case — three of the seven actions destroy the shadow
altogether. And the shadow is hardly ever exactly the same size as the object; it is usually bigger,
and it keeps the object's outline only when the object faces the light squarely.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

ACTION OBSERVATIONS REGARDING SHADOW

The screen is removed. No shadow is seen. The light simply travels on into the room; with nothing to
catch it, there is nothing on which the dark patch can appear.

The object is removed. No shadow. The screen shows only a bright circle of torch light.

The torch is switched off. No shadow — there is no light to be blocked.

The object is moved closer to the The shadow becomes smaller and its edges become sharper. Its size comes
screen, keeping the torch and the close to the size of the object.
screen fixed.

The object is moved closer to the The shadow becomes larger and its edges become blurred.
torch, keeping the torch and the
screen fixed.

The object is tilted, keeping the The shape of the shadow changes. A round disc, for example, gives a circle
torch and the screen fixed. when it faces the torch, an oval when it is tilted, and almost a straight line
when its edge faces the torch.

The colour of the object is changed. No change at all. The shadow stays dark, of the same shape and size. A red
ball and a green ball of the same size cast exactly the same shadow.

Object near the torch — big shadow

large

Object near the screen — small shadow

small

The rays spread out from the torch. An object placed near the torch cuts off a wide cone of light, so its
shadow on the wall is large; the same object near the wall cuts off only a narrow cone, so its shadow
is small.

Page 13 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
a g l AglaSem · NCERT Solutions

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What conclusions do you draw from this activity? What do we need to observe a
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Three things are needed to observe a shadow:
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a source of light + an opaque object + a screen → shadow

Take away any one of the three and the shadow disappears. In everyday life the wall, the floor,
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No — the colour of the shadow does not change when the colour of the object is changed.
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The shadow of a red ball and of a blue ball is the same dark patch.
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Why it happens: A shadow is not made of the object; it is only the region where the

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object's body has stopped the light from reaching the screen. Since “no light” has no
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11.5 Reflection of Light
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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Light from torch → steel plate → reflected → bright spot on the opposite wall

Behind the plate → no light → shadow

Why it happens: A rough, dull surface such as cardboard scatters the light it
receives in all directions, so no bright patch is formed anywhere. A smooth, polished
surface sends almost all the light away together in one direction. This change of
direction of light by a shiny surface is called the reflection of light.

Activity 11.5: Let us investigate — Pages 159 & 160
11.5 Reflection of Light

ACTIVITY

Q1 Take it outside and let the sunlight fall on the shiny surface. What can you do to
redirect light on the wall on which the sunlight is not falling directly?

Hold the plane mirror (or the shiny steel plate) in the sunlight and slowly turn and tilt it until
the patch of light it throws lands on the shaded wall.
Sunlight falling on the mirror is reflected. By changing the way the mirror faces, you change the
direction in which the reflected light goes — so you can steer that bright patch on to a wall
which the Sun itself cannot reach.

Caution: Never direct the reflected sunlight into anyone's eyes.

Page 15 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q2 Turn the shiny plate or mirror in different directions to redirect the light onto a wall
or a nearby surface (Fig. 11.8). Do you see a spot of light on the wall? Does it mean
that the shiny plate or mirror has changed the direction of light?

Sun

bright spot of light
sunlight

reflected light

mirror

wall

Fig. 11.8, page 160 (redrawn sketch): a shiny plate or mirror turns sunlight onto a
shaded wall, where a bright spot appears.

Yes — a bright spot of light appears on the wall, and yes, it does mean that the mirror has
changed the direction of the light.

Why it happens: Sunlight comes down to the mirror along one straight line. It
cannot reach the shaded wall by itself, because nothing bends it. When it strikes the
polished surface, it is turned away along a new straight line, and that new line ends
on the wall. The bright spot is proof that the light has been reflected — sent back in
a different direction.

Q3 Now, tilt the shiny plate or mirror in different ways and observe the light spot on
the wall. Does it change position?

Yes. Each time the mirror is tilted, the bright spot jumps to a new place on the wall. A small tilt
of the mirror moves the spot a long way.

Page 16 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: The direction of the reflected light depends on how the mirror is
turned. Tilt the mirror and the reflected ray swings round with it, so the spot shifts.
Between the mirror and the wall, though, the light still travels perfectly straight —
light always travels in straight lines and changes direction only where it meets the
mirror.

Conclusion of the activity: A shiny surface or a mirror changes the direction of the
light that falls on it. This change in direction of light by a mirror is called the
reflection of light.

Activity 11.6: Let us experiment — Page 160

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

11.5 Reflection of Light

ACTIVITY

Q1 Now, place the mirror in the path of the light beam while keeping the comb steady
(Fig. 11.9b). What do you observe?

plane mirror

reflected beam incident beam

normal

torch

white paper
comb with one slit open

Fig. 11.9(b), page 160 (redrawn sketch): the thin beam from the slit falls on the plane
mirror and leaves along a new straight line.

The thin beam that was running straight along the paper bends away at the mirror and
travels off in a new direction. Two straight beams are now seen on the paper — the one going
to the mirror and the one coming away from it — meeting at the point where the mirror stands.

Page 18 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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Why it happens: The path of the light beam is changed after falling on the mirror —
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Tip: Keep the comb steady and turn only the mirror. You will see the reflected beam
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In-text Question — Page 160
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11.5 Reflection of Light

Q1 In a mirror, I can also see my face. Is that also due to the reflection of light?
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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: A plane mirror is very smooth, so all the rays from one point of
your face are reflected in an orderly way and appear to come from one point behind
the mirror. A wall is rough and scatters the rays in every direction, so no image is
formed on it — which is why you cannot see your face in a wall.

Activity 11.7: Let us experiment — Page 161
11.6 Images Formed in a Plane Mirror

ACTIVITY

Q1 Place the pen in front of the mirror as shown in Fig. 11.10. What do you see in the
mirror?

plane mirror

image of the pen

pen (object)

table

Fig. 11.10, page 161 (redrawn sketch): a pen standing on the table in front of a plane
mirror, and its image seen in the mirror.

A second pen is seen, standing behind the mirror, looking exactly like the real one.
The pen you have kept on the table is the object; the pen that seems to be behind the mirror is
its image formed by the mirror.

Page 20 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: Light from every point of the pen falls on the mirror and is
reflected to your eye. The reflected rays reach your eye as if they had started from a
point behind the mirror. There is really no pen there — but your eye cannot tell the
difference, and you see an image.

Q2 Now, move the pen to different positions in front of the mirror and compare the
sizes of the images of the pen at each position. Are the two sizes the same?

Yes. At every position the image is exactly as big as the pen itself.

size of image = size of object

Bring the pen close to the mirror or take it far away — the image never grows or shrinks
compared with the object.

Check it yourself: Hold a 15 cm scale against the mirror. Its image also reads 15 cm
long. This is why a plane mirror is the right mirror for dressing up, and why a curved
mirror (like the back of a steel spoon) is not.

Q3 Again, move the pen to different positions in front of the mirror and observe if the
image is upright at each position. Does the tip of the pen appear on top at each
position?

Yes. The tip of the pen appears on top in the image at every position — the image is never
upside down.
An image whose top and bottom are the same way up as the object's is called an erect image.
The image formed by a plane mirror is erect.

Tip: Do not confuse erect with unchanged. The mirror image is the right way up, but
it is still turned round left-to-right — that is lateral inversion, which you meet in
Activity 11.8.

Page 21 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q4 Now, place a screen vertically behind the mirror. Move it around. Do you get the
image on the screen? Repeat this by placing the screen in front of the mirror.

plane mirror

image of the pen

pen (object)

table

Fig. 11.10, page 161 (redrawn sketch): a pen standing on the table in front of a plane
mirror, and its image seen in the mirror.

No. The image cannot be caught on the screen — neither behind the mirror nor in front of it.
The screen shows nothing, however you move it.

Why it happens: The reflected rays do not really meet behind the mirror; they only
appear to come from there. Since no light actually reaches the place where the
image seems to be, there is nothing for a screen to catch. Such an image is called a
virtual image — the image formed by a plane mirror cannot be obtained on a
screen.

Compare: The pinhole camera of Section 11.7 is the opposite case — there the rays
really do meet on the tracing paper, so that image can be caught on a screen.

Activity 11.8: Let us experiment — Pages 161 & 162

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

11.6 Images Formed in a Plane Mirror

ACTIVITY

Q1 Now, stand close to the mirror. Is the image also closer to the mirror?

plane mirror

you your image in the mirror

Fig. 11.11, page 161 (redrawn sketch): a student standing in front of a plane mirror,
looking at his own image in it.

Yes. When you stand close to the mirror, your image also appears close to the mirror — just
behind it. Step back, and the image goes back by the same amount.

Try This: Walk slowly towards a mirror. Your image walks towards you at the same
speed, so the gap between you and your image closes twice as fast as your own
steps.

Page 23 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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Stand at different distances from the mirror and notice how far the image appears
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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

d d

object image

mirror

The image in a plane mirror is always as far behind the mirror as the object is in front of it, and it is of
the same size.

Q3 Raise your left arm. Which arm does your image raise? Touch your right ear. Which
ear does your image touch?

Raise your left arm and the image raises what looks like its right arm. Touch your right ear and
the image touches what looks like its left ear.
This left–right swap in a mirror image is called lateral inversion. There is lateral inversion in
the images formed by a plane mirror.

Why it happens: The mirror does not really turn you round; it simply sends back
each point of you straight across the mirror. The point nearest your left side comes
back on the side we call the image's right. So sides are exchanged, while top and
bottom are not — the image stays erect.

Did you know? This is why AMBULANCE is painted reversed on the front of the van.
A driver ahead sees it in the rear-view mirror, where lateral inversion turns it back
into ‘AMBULANCE’, easy to read at a glance.

In-text Question — Page 162

Page 25 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

11.7 Pinhole Camera

Q1 Can we see an image of an object only in a mirror or are there some other ways as
well?

A mirror is not the only way. Images can be formed in several other ways:

By a pinhole camera — light through a tiny hole makes an inverted image on a screen
(Section 11.7).
By any still water surface — a pond, a lake or a bucket of water acts like a mirror and shows
reflections.
By other polished surfaces — a steel plate, a shiny tile, a car's windscreen, a glass window
at night.
By lenses — as in a magnifying glass, spectacles or a camera, which you will study in higher
classes.

Tip: There is one big difference. A mirror image is erect and cannot be taken on a
screen; a pinhole-camera image is upside down and can be taken on a screen.

Activity 11.9: Let us explore — Page 163
11.7 Pinhole Camera

ACTIVITY

Q1 What do you see on the screen? Do you notice anything surprising?

On the screen we see a small, faint image of the candle flame. The surprising part is that the
image is upside down — it is inverted. The tip of the flame in the image points downwards.

Page 26 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

pinhole

screen

candle

Light from the top of the flame goes down through the pinhole and lands low on the screen; light
from the bottom goes up and lands high. The rays cross at the hole, so the image is inverted.

Why it happens: Light travels in straight lines, and only the rays that pass through
the tiny hole reach the screen. The straight ray from the top of the flame can only
continue downwards after the hole, and the ray from the bottom of the flame can
only continue upwards. Since the two rays cross each other at the pinhole, top and
bottom are exchanged and the image comes out upside down.

Tip: Make the hole smaller and the image gets sharper but dimmer; make it bigger
and the image gets brighter but blurred.

Activity 11.10: Let us construct — Page 163
11.7 Pinhole Camera

ACTIVITY

Q1 Do the images seen in the camera show the colours of the objects on the other
side? Are the images erect or upside down?

Yes, the images show the natural colours of the objects — green leaves look green, a red
building looks red. And the images are upside down (inverted), not erect.

Page 27 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Pinhole camera image → coloured, inverted, formed on a screen, smaller or larger

depending on how far the screen is

Why it happens: The pinhole does not change the light in any way, it merely lets a
narrow bundle through — so every colour reaching the hole is carried straight on to
the tracing paper. The inversion comes from the crossing of the straight rays at the
hole, exactly as in Activity 11.9.

Try This: Slide the smaller box in and out. Pulling it out (screen farther from the
pinhole) makes the image bigger but dimmer. This is why the sliding box is used at
all.

Let Us Enhance Our Learning — Pages 165 to 167
Chapter exercises

LET US ENHANCE OUR LEARNING

Q1 Which of the following are luminous objects? Mars, Moon, Pole Star, Sun, Venus,
Mirror

The luminous objects are the Pole Star and the Sun.

OBJECT LUMINOUS / NON-LUMINOUS REASON

Mars Non-luminous A planet; shines only by reflecting sunlight

Moon Non-luminous Reflects the sunlight falling on it

Pole Star Luminous A star — it emits its own light

Sun Luminous Our nearest star; the main natural source of light

Venus Non-luminous A planet; shines by reflected sunlight

Mirror Non-luminous It only reflects the light that falls on it

Page 28 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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co m
m.
Tip: Brightness is not the test. Venus is the brightest object in our night sky after the

m as e
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Moon, yet it makes no light of its own.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q3 Sahil, Rekha, Patrick, and Qasima are trying to observe the candle flame through
the pipe as shown in Fig. 11.16. Who can see the flame?

Sahil

Rekha

candle

Patrick
Qasima

Fig. 11.16, page 166: four students look through the branched pipe at the candle flame.

Only Rekha can see the flame.
In Fig. 11.16 the candle stands at the right-hand end of the pipe. Rekha's eye is at the far end of
the straight horizontal limb that runs directly to the candle, so there is an unbroken straight
path from the flame to her eye.

STUDENT CAN THE FLAME REASON
BE SEEN?

Sahil No His limb of the pipe is set at an angle to the straight limb — the
light would have to turn a corner

Rekha Yes Her limb is straight and in line with the candle flame

Patrick No His limb also meets the main pipe at an angle

Qasima No Her limb hangs down at right angles; light will not bend down
into it

Page 30 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: Light travels in a straight line. It cannot go round the bends of the
branched pipe. Only the person whose eye, the pipe and the flame lie on one
straight line receives the light — that is Rekha.

Q4 Look at the images shown in Fig. 11.17 and select the correct image showing the
shadow formation of the boy.

(a) (b) (c) (d)

Fig. 11.17, page 166: four pictures of a boy standing in the Sun, with the Sun in a
different place in each.

The correct image is (d).
A shadow always forms on the side of the object opposite to the light source, along the straight
line drawn from the source through the object. In (d) the Sun is high up on the right, and the
boy's shadow stretches away to the lower left, joined to his feet. That is exactly what really
happens.

OPTION WHERE IS THE WHY IT IS WRONG / RIGHT
SUN?

(a) Almost straight Wrong — with the Sun overhead the shadow should be short and near
overhead the feet, not long

(b) Top left Wrong — the shadow is drawn right under the boy instead of towards
his right

(c) Top right Wrong — the shadow is drawn towards the same side as the Sun

(d) Top right Correct — shadow falls to the opposite (left) side, starting at his feet

Page 31 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Check it yourself: Stand in the Sun and draw an imaginary straight line from the
Sun through your head. It hits the ground exactly where the top of your shadow lies.

Q5 The shadow of a ball is formed on a wall by placing the ball in front of a fixed torch
as shown in Fig. 11.18. In scenario (i) the ball is closer to the torch, while in scenario
(ii) the ball is closer to the wall. Choose the most accurate representation of the
shadows formed in both scenarios from the options provided (a and b).

(i) (a)

ball

(ii) (b)

torch
wall (screen)

Fig. 11.18, page 166: (i) the ball close to the torch, (ii) the ball close to the wall; options
(a) and (b) show the shadow on the wall.

Scenario (i) → option (b) (the large shadow), and scenario (ii) → option (a) (the small shadow).

Ball near the torch → large shadow, blurred edge

Ball near the wall → small shadow, sharp edge

Why it happens: The light from a torch spreads out as a cone. A ball held close to
the torch stands where the cone is still narrow, so it blocks a big share of the beam
and its shadow, spread out on the far wall, is large. The same ball held close to the
wall blocks only a small part of the wide beam, so the shadow is small and nearly the
size of the ball itself.

Page 32 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Try This: Hold your fist between a torch and the wall and walk it slowly from the
torch to the wall. The shadow shrinks steadily and its edges become sharper.

Q6 Based on Fig. 11.18, match the position of the torch in Column A with the
characteristics of the ball's shadow in Column B. Column A: If the torch is close to
the ball; If the torch is far away; If the ball is removed from the set-up; If two
torches are present in the set-up on the left side of the ball. Column B: The shadow
would be smaller; The shadow would be larger; Two shadows would appear on the
screen; A bright spot would appear on the screen

(i) (a)

ball

(ii) (b)

torch
wall (screen)

Fig. 11.18, page 166: (i) the ball close to the torch, (ii) the ball close to the wall; options
(a) and (b) show the shadow on the wall.

COLUMN A COLUMN B

If the torch is close to the ball The shadow would be larger

If the torch is far away The shadow would be smaller

If the ball is removed from the set-up A bright spot would appear on the screen

If two torches are present in the set-up on the left side of the ball Two shadows would appear on the screen

Page 33 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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co m
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Why these pairs: A torch held close to the ball throws a steeply spreading cone of

m l a se
light, so the ball's shadow on the wall is stretched out and large. From far away the
o
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rays reaching
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g bright patch of the torch. Two torches send light from two slightly different
smaller.
athe
directions, so the ball casts a separate shadow for each — two shadows.
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Did you know? A cricket player under floodlights has several shadows for exactly
this reason — one for each floodlight tower.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q7 Suppose you view the tree shown in Fig. 11.19 through a pinhole camera. Sketch the
outline of the image of the tree formed in the pinhole camera.

Fig. 11.19, page 167: the tree to be viewed through a pinhole camera.

The image is an upside down (inverted) outline of the same tree — the pointed top of the
leafy crown now points downwards and the trunk sticks up.

Page 35 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

the tree (object) image on the screen

A pinhole camera turns the picture upside down: the crown of the tree appears at the bottom of the
image and the trunk at the top.

Why it happens: Light from the top of the tree travels in a straight line through the
pinhole and continues downwards to the lower part of the screen. Light from the
foot of the trunk travels up through the hole and lands on the upper part of the
screen. The straight rays cross one another at the pinhole, so the whole picture is
turned upside down. Its shape and colours stay the same.

Tip: Draw the tree lightly on your page, then turn the page upside down and trace it
— that traced figure is the pinhole image.

Q8 Write your name on a piece of paper and hold it in front of a plane mirror such that
the paper is parallel to the mirror. Sketch the image. What difference do you notice?
Explain the reason for the difference.

The name in the mirror is reversed from left to right. The letters keep the right way up, but the
word runs backwards and each letter looks turned about — you have to read it from the other
end.

Page 36 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

ANITA ATINA
on the paper as seen in the mirror

mirror
The mirror image of a written name is laterally inverted — left and right are interchanged, top and
bottom are not.

Why it happens: This difference is due to lateral inversion. A plane mirror sends
every point of the paper straight back across itself, so the side of the paper that was
on your left appears on the right in the image. The letters are therefore swapped
side to side. They are not turned upside down, because the mirror does not
exchange top and bottom.

Try This: Write a name made only of the letters A, H, I, M, O, T, U, V, W, X, Y — such
as TOM or MAMA. Its mirror image reads exactly the same, because each of these
letters is symmetric about a vertical line.

Q9 Measure the length of your shadow at 9 AM, 12 PM, and 4 PM with the help of your
friend. Write down your observations: (i) At which of the given times is your shadow
the shortest? (ii) Why do you think this happens?

Stand at the same spot each time, let your friend mark the tip of your shadow, and measure
from your feet to the mark with a measuring tape. A typical set of readings looks like this:

TIME POSITION OF THE SUN LENGTH OF SHADOW (SAMPLE)

9 AM Low in the eastern sky About 2 m — long, pointing west

12 PM (noon) Highest in the sky About 0.5 m — shortest

4 PM Low in the western sky About 2.5 m — long, pointing east

(i) The shadow is the shortest at 12 PM (around noon).

Page 37 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

(ii) Because at noon the Sun is at its highest position in the sky. Sunlight then comes down
almost vertically, so the portion of the ground that your body screens off is small and the
shadow is short. In the morning and in the late afternoon the Sun is low, its rays come slanting,
and the same body blocks a long strip of ground — so the shadow is long.

Check it yourself: Repeat the measurement in December and again in June. The
noon shadow is longer in winter, because even at noon the Sun does not climb as
high in the sky.

Q10 On the basis of following statements, choose the correct option. Statement A:
Image formed by a plane mirror is laterally inverted. Statement B: Images of
alphabets T and O appear identical to themselves in a plane mirror. (i) Both
statements are true (ii) Both statements are false (iii) Statement A is true, but
statement B is false (iv) Statement A is false, but statement B is true

The correct option is (i) Both statements are true.

Statement A is true — every image formed by a plane mirror is laterally inverted; your left
appears as the image's right.
Statement B is true — the letters T and O are symmetric about a vertical line drawn
through their middle. Swapping their left and right halves gives back the same letter, so their
mirror images look identical to themselves.

Why it happens: Lateral inversion always takes place, but you can only notice it
when the two halves of the shape are different. T and O have matching halves, so
the swap leaves no trace. Letters such as B, F, P, R, S and the digit 3 have unlike
halves, so their mirror images look clearly reversed.

Tip: The full set of capital letters that read the same in a plane mirror is A, H, I, M, O,
T, U, V, W, X, Y.

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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co m
m.
Suppose you are given a tube of the shape shown in the Fig. 11.20 and two plane
e
Q11

o m If yes, mark where you will fix the plane mirrors. glas
mirrors smaller than the diameter of the tube. Can this tube be used to make a
c
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a Fig. 11.20, page 167: the tube supplied — both open ends face the same side.

se m
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Yes, this tube can be used to make a periscope. Fix one plane mirror at each of the two bends
(corners) of the tube, each tilted at 45° to the axis of the tube, with the shining surfaces facing

co m
into the tube so that one mirror looks at the other.
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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

light from the object
mirror 1 (45°)

to the eye mirror 2 (45°)

A plane mirror at 45° at each bend turns the light through 90° twice, so it travels along the whole
tube and reaches the eye.

Why it happens: Light will not turn a corner by itself, but a mirror can turn it. Light
from the object enters the upper opening and runs straight along the top arm. The
first 45° mirror sends it down the vertical arm; the second 45° mirror sends it along
the lower arm into your eye. This is the same double reflection that works in the Z-
shaped periscope of Fig. 11.14, so the tube does the job of a periscope — it lets you
see an object that you cannot see directly.

Tip: Both mirrors must be smaller than the tube's diameter (as given) so that they fit
inside, and each must be fixed exactly across a corner — a mirror placed anywhere
along a straight part of the tube would simply block the light.

Page 40 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Q12 We do not see the shadow on the ground of a bird flying high in the sky. However,
the shadow is seen on the ground when the bird swoops near the ground. Think
and explain why it is so.

Because the shadow of the bird gets bigger and fainter the higher the bird flies, until it is too
faint to notice at all; close to the ground the same shadow is small, dark and sharp.

Bird high in the sky → shadow very large and extremely faint → not seen

Bird near the ground → shadow small, dark and sharp → clearly seen

Why it happens: The Sun is not a point — it is a broad source of light. When the bird
is far above the ground, sunlight coming from all parts of the Sun's disc spreads
around the small body of the bird and reaches almost every point of the ground
below it. Practically no place is left in complete darkness, so the shadow is smeared
over a large area and becomes so faint that it disappears into the brightness of the
sunlit ground. When the bird swoops down, there is little room for the light to
spread behind it, so a small, well-defined patch of the ground gets no light and we
see a sharp dark shadow.

Check it yourself: Hold your finger a few centimetres above a sunlit page — you get
a sharp shadow. Raise it to arm's length and the shadow becomes a large, pale blur.

Exploratory Projects — Pages 167 & 168
Interdisciplinary projects

EXPLORATORY PROJECTS

Q1 Have you ever seen a firefly where you live? If no, ask your elders if fireflies were
seen earlier in your region. If yes, find out the reasons for their not being seen
anymore. Develop a story about it.

How to do this project: talk to two or three elders of your family or locality. Ask them where
and in which months they used to see fireflies, whether the number has fallen, and what has
changed in that place since — new street lights, buildings, cutting of trees, use of pesticides.
Note their answers, then weave them into a short story.

Page 41 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Reasons usually found for the disappearance of fireflies:

Light pollution — bright street lights and hoardings drown out the firefly's own flashes, so
males and females can no longer find each other.
Loss of forest and grass cover — fields, hedges and moist leaf litter where the larvae live
are cleared for houses and roads.
Pesticides and insecticides — these kill fireflies and also the snails and small insects their
larvae feed on.
Excessive tourism and noise in firefly-watching areas, and drying up of ponds and streams
nearby.

Sample answer (a short story): “My grandmother says that when she was ten, the
guava orchard behind our house would light up on July nights with hundreds of tiny
green lamps. The children called them jugnu and caught them in glass jars, then let
them go before sleeping. Today a tall pole light stands where the orchard was. The
night never becomes dark, and the jugnu have not come back for many years.
Grandmother says the fireflies did not go away — we took away their darkness.” End
your story with one thing your family will do, such as switching off the outdoor light
at night.

Q2 Repeat Activity 11.4, but this time cover the face of the torch with a coloured
transparent paper and observe the colour of the shadow. Repeat this using
transparent paper of different colours. Report your conclusions.

What you will observe:

COLOUR OF PAPER ON THE COLOUR OF THE LIT PART OF COLOUR OF THE
TORCH THE SCREEN SHADOW

Red Red Dark (black)

Green Green Dark (black)

Blue Blue Dark (black)

Yellow Yellow Dark (black)

Conclusions: The coloured paper changes the colour of the light, and therefore the colour of
the bright region around the shadow. The shadow itself stays dark in every case — its shape
and size do not change either. A shadow has no colour of its own, because it is only a place
where no light has reached.

Page 42 of 46

Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Try This: Use two torches, one covered with red paper and the other with green,
placed a little apart. Each throws its own shadow, and each shadow is lit by the other
torch — so you get one reddish and one greenish patch instead of black. A beautiful
result to show your class.

Q3 A plane mirror forms only a single image of an object. But what will happen if two
or more mirrors are kept at an angle with each other or parallel to each other? Find
out by placing two mirrors as shown in Fig. 11.21.

images

plane mirror plane mirror

90°

object (bottle cap)

Fig. 11.21, page 168 (redrawn sketch): two plane mirrors standing at right angles on a
table with a bottle cap in front of the corner.

Two mirrors give many images, because each mirror also forms images of the images made by
the other — reflections of reflections. The number depends on the angle between the mirrors.

Number of images = (360° ÷ angle between the mirrors) − 1

Page 43 of 46

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Class 7 Science Chapter 11 Light: Shadows and Reflections
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ANGLE BETWEEN THE TWO MIRRORS NUMBER OF IMAGES SEEN

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Place a bottle cap between two mirrors joined at 90°, exactly as in Fig. 11.21, and count — you

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Why it happens: The first mirror forms an image of the cap. That image acts as an
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agl
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reflection adds more images, until the mirrors run out of room to reflect. When the
a g
mirrors are parallel, the reflections never run out — they only get fainter and fainter,
because a little light is lost at every reflection.

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Did you know? The kaleidoscope of Section 11.8.2 uses three mirrors at 60° to each
a g l
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other, which is why it fills with so many symmetric patterns.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Why it happens: The size of the image does not depend on the size of the mirror.
Light from every part of the tree falls on the small mirror and is reflected; the mirror
forms a complete image of the tree behind itself, of the same size as the tree. Your
eye, however, can only receive the rays that actually pass through the small piece —
so the mirror acts like a little window on to that image. Move your eye or the mirror
and you see through a different part of the window.

Check it yourself: Look at your face in a small mirror held close to your eye — you
see only your eye. Now stretch your arm out; the same little mirror shows your
whole face. The farther the mirror, the wider the view it gives.

Chapter at a glance
Objects that give out their own light — the Sun, stars, lightning, fire, fireflies, a lit bulb —
are luminous. Objects that only send back the light falling on them, such as the Moon, a
mirror, Mars or Venus, are non-luminous.
Light travels in a straight line. The matchbox activity (three holes in a line), the straight-
versus-bent pipe and the laser beam in milky water all point to the same conclusion.
Light passes almost completely through transparent materials, partly through translucent
materials, and not at all through opaque materials.
A shadow is the dark patch formed where an object blocks light. Three things are needed —
a source of light, an opaque object and a screen. The shadow shows only the outline;
changing the colour of the object never changes the colour of its shadow.
A mirror changes the direction of light — this is the reflection of light. The image in a
plane mirror is the same size as the object, erect, cannot be caught on a screen, is as far
behind the mirror as the object is in front, and is laterally inverted.
A pinhole camera forms a real, upside down (inverted) image on its screen because rays
from the top of the object cross the rays from the bottom at the pinhole. Two plane mirrors
make a periscope; three make a kaleidoscope.

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Class 7 Science Chapter 11 Light: Shadows and Reflections AglaSem · NCERT Solutions

Quick revision

TERM WHAT IT MEANS EXAMPLE FROM THE POINT TO
CHAPTER REMEMBER

Luminous An object that emits its own Sun, Pole Star, lightning, firefly, The Moon is not
object light LED lamp luminous

Non-luminous An object that does not emit Moon, mirror, Mars, Venus, a It is seen by the light it
object light of its own book reflects

Transparent Light passes almost Clear glass, water You can see through it
completely through it clearly

Translucent Light passes partly through it Tracing paper, thin cloth, frosted Makes a lighter, blurred
glass shadow

Opaque Light does not pass through it Cardboard, thick cloth, a steel Makes the darkest
plate shadow

Shadow Dark patch formed where an Your shadow on the ground in Needs source + object +
opaque object blocks light the Sun screen

Reflection of The change in direction of Sunlight thrown on a shaded Light still travels in
light light by a mirror wall by a steel plate (Fig. 11.8) straight lines

Plane mirror A flat, not curved, mirror The mirror you comb your hair Image: same size, erect,
in virtual

Lateral Left of the object appears as AMBULANCE written in reverse Letters T, O, A, M look
inversion right in the image on vans unchanged

Pinhole camera A box in which light through Candle flame image in Fig. The image is upside
a tiny hole forms an image 11.12 down

Periscope Z-shaped box with two plane Used in submarines, tanks, Lets you see what is
mirrors bunkers hidden

Kaleidoscope Tube with three mirror strips Fig. 11.15 Reflections of
and coloured bits reflections make
patterns

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