NCERT Solutions Curiosity Chapter 11 Chapter exercises — Let Us Enhance Our Learning

Book page 165 to 167 Updated on2026-09-05

Q1.

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

Answer

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

Tip: Brightness is not the test. Venus is the brightest object in our night sky after the Moon, yet it makes no light of its own.

Q2.

Match the items in Column A with those in Column B. Column A: Pinhole camera, Opaque object, Transparent object, Shadow. Column B: Blocks light completely, The dark region formed behind the object, Forms an inverted image, Light passes almost completely through it

Answer

Column A	Column B
Pinhole camera	Forms an inverted image
Opaque object	Blocks light completely
Transparent object	Light passes almost completely through it
Shadow	The dark region formed behind the object

Why these pairs: Rays from the top and the bottom of an object cross at the pinhole, so the pinhole camera turns the picture upside down. An opaque body lets no light through at all, while a transparent one lets almost all of it through. The dark region left behind an object where light could not reach is exactly what we call its shadow.

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?

Answer

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 be seen?	Reason
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

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.

Answer

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 Sun?	Why it is wrong / right
(a)	Almost straight overhead	Wrong — with the Sun overhead the shadow should be short and near 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

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).

Answer

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.

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

Answer

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

Why these pairs: A torch held close to the ball throws a steeply spreading cone of light, so the ball's shadow on the wall is stretched out and large. From far away the rays reaching the ball are nearly parallel, so the shadow is close to the size of the ball — smaller. With no ball there is nothing to block the light, and the wall shows only the bright patch of the torch. Two torches send light from two slightly different directions, so the ball casts a separate shadow for each — two shadows.

Did you know? A cricket player under floodlights has several shadows for exactly this reason — one for each floodlight tower.

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.

Answer

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.

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.

Answer

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.

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?

Answer

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).

(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

Answer

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.

Q11.

Suppose you are given a tube of the shape shown in the Fig. 11.20 and two plane mirrors smaller than the diameter of the tube. Can this tube be used to make a periscope? If yes, mark where you will fix the plane mirrors.

Answer

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.

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.

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.

Answer

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.

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