NCERT Solutions for Class 7 Science Chapter 11 Light Shadows and Reflections (PDF) – 2027

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.

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

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.

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

Yes. Some other ways are:

• Straight and bent pipe (Activity 11.2) — a candle flame is seen through a straight pipe but not through a bent pipe.
• Laser beam in milky water (Dive Deeper, page 156) — the beam is seen as a straight line.
• Shadows — an object blocks the straight rays, and a shadow of its outline forms behind it.

No, the flame cannot be seen through the bent pipe — even though the flame is still burning at the same place and the pipe still points at it.

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.

It depends on the material the object is made of:

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

The prediction should follow from the kind of material:

• Glass or clear plastic — yes, the spot of light will still be seen, almost as bright as before.
• Tracing paper or thin cloth — the spot will still be there but dim and blurred.
• Cardboard, thick cloth or a steel plate — no, the spot will disappear and a dark patch (a shadow) will take its place.

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:

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.

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.

It was formed because light travels in a straight line. The opaque object stopped the light going towards that part of the wall, and light cannot bend around the object to reach it. So that part stayed dark — this dark patch is the shadow.

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

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.

Three things are needed to observe a shadow:

Take away any one of the three and there is no shadow. The walls, the floor or the ground act as the screen in daily life. The shape, size and sharpness of a shadow depend on the position of the object relative to the light source and the screen.

No — the colour of the shadow does not change when the colour of the object is changed.

Because a polished steel plate does two things at the same time. It is opaque, so it stops the light and makes a shadow behind it. It is also shiny, so it does not absorb that light — it sends the light off in a new direction (this is reflection of light), and this light makes a bright spot on the opposite wall.

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.

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.

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.

The thin beam that was running straight along the paper changes its direction at the mirror and goes off along a new straight line. So the path of the light beam is changed after falling on the mirror — the reflection of light takes place at the mirror.

Yes. Seeing your face in a mirror is exactly the same effect as the bright spot on the wall — it is reflection of light.

Light from a lamp or from the Sun falls on your face. Your face sends this light in all directions; some of it reaches the mirror, and the mirror reflects it back to your eyes. Your brain judges the light to be coming from behind the mirror, and you see a face there — your image.

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.

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

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

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.

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. The image formed by a plane mirror cannot be obtained on a screen.

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.

Yes — a very simple one:

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.

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

• A pinhole camera — light through a tiny hole forms an upside-down image on a screen (Section 11.7).
• Still water — a pond, a lake or a bucket of water shows images like a mirror.
• Other shiny surfaces — a steel plate, a polished tile, a glass window at night.
• Lenses — in a magnifying glass, spectacles or a camera (you will study these in higher classes).

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.

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.

The luminous objects are the Pole Star and the Sun.

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.

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.

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

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.

In the mirror the name appears reversed from left to right. The letters stay upright (not upside down), but the word reads from right to left, and letters such as N, R, S and J look turned round.

Reason: This is due to lateral inversion. A plane mirror interchanges the left and right sides of an object in its image, but not its top and bottom.

Sample observations (your own readings will differ):

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

(ii) At noon the Sun is at its highest position in the sky, so its light falls almost straight down and the body blocks light from only a small patch of ground — the shadow is short. In the morning and afternoon the Sun is low, its rays come slanting, and the shadow is long.

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.

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 into the tube so that one mirror looks at the other.

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.

Reasons usually found: light pollution from street lights and hoardings, cutting of forests and bushes, use of pesticides, and too much tourism and noise.

What you will observe:

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.

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.

Place a bottle cap between two mirrors joined at 90°, exactly as in Fig. 11.21, and count — you will see three images along with the cap itself. Close the mirrors to 60° and the count rises to five.

Prediction and result: yes, it can. Take a small piece of mirror outdoors, hold it at arm’s length and move your eye about behind it — you can see the whole tree in it, bit by bit, and from a suitable position the whole tree at once.