Light: Shadows and Reflections
Every in-text question and end-of-chapter exercise from the chapter, answered directly — from luminous objects and straight-line propagation to shadows, mirrors, and pinhole cameras.
In-Text Questions
Questions woven through the chapter narrative — activities, “Dive Deeper” prompts, and Keshav & friends’ curiosity boxes.
Does the Moon actually produce its own light? Is moonlight just reflected sunlight? Which objects give off their own light? — Keshav’s question, watching the moonlit landscape from the bus
Fig 11.1 — Natural sources of light
Fig 11.2 — Fire, an early artificial sourceNo — the Moon does not produce its own light. It is a non-luminous object: it only reflects the light of the Sun that falls on it, so moonlight is indeed just reflected sunlight.
- Luminous objects emit their own light — the Sun, stars (like the Pole Star), lightning, natural fire, and certain animals such as fireflies.
- Non-luminous objects do not emit their own light — they are visible only because they reflect light from a luminous source. The Moon, planets, a mirror, and most everyday objects around us fall in this category.
So of all the objects in our solar system apart from the Sun, none produce their own light — they all shine only by reflecting sunlight, exactly as Keshav recalled from “Beyond Earth”.
Move one of the three matchboxes slightly to a side or up and down. Are you able to obtain the light spot on the screen now?
No — once even one of the three holes is out of line, the bright spot disappears from the screen. This shows that light can only pass through when all three holes lie exactly along one straight line, which suggests that light travels in a straight line.
Now bend the pipe and try to see the candle flame again. Can you still see it?
Fig 11.5a — Straight pipe
Fig 11.5b — Bent pipeNo — the candle flame is visible through a straight pipe but disappears the moment the pipe is bent. This confirms once again that light travels in a straight line, since it cannot follow the bend in the pipe to reach the eye.
Pass a laser beam through a beaker filled with water in which a drop of milk is added. What do you observe? Do you see that the beam of laser light inside water follows a straight path?
Yes — the drop of milk scatters the laser light so that its path becomes visible, and it shows up as a straight, narrow line crossing the beaker, confirming that light travels in a straight line even inside water.
Interesting extension: light can sometimes bend around corners too (a phenomenon called diffraction) — but that is something explored in higher grades.
Place objects made of different materials in the path of light from a torch. What conclusions could you draw about transparent, translucent, and opaque materials?
| Material | Classification | Light passes |
|---|---|---|
| Cardboard | Opaque | Not at all |
| Paper (plain sheet) | Translucent | Partially |
| Glass (clear) | Transparent | Fully |
| Tracing paper | Translucent | Partially |
| Thick cloth | Opaque | Not at all |
Conclusion: Light passes almost completely through transparent materials, partially through translucent materials, and not at all through opaque materials.
What happens when an opaque object blocks the path of light? Why is a dark patch formed on the screen?
Fig 11.7 — Shadows around us
Fig 11.7 — Shadows of friendsSince light travels in a straight line, placing an opaque object in its path blocks the light completely from reaching the region directly behind the object.
The dark patch where light does not reach is called the shadow. Opaque objects form darker shadows, translucent objects form lighter shadows, and even some transparent objects can create faint shadows.
Record your observations regarding the shadow for each action listed in Table 11.2.
| Action | Observation regarding shadow |
|---|---|
| The screen is removed | No shadow can be observed (nothing to catch the blocked light) |
| The object is removed | No shadow is formed; only a bright spot of light appears |
| The torch is switched off | No shadow is formed, since there is no light to be blocked |
| Object moved closer to screen (torch, screen fixed) | The shadow becomes smaller and sharper |
| Object moved closer to torch (torch, screen fixed) | The shadow becomes larger and more blurred |
| Object tilted (torch, screen fixed) | The shape and size of the shadow change |
| Colour of the object changed | The colour of the shadow does not change — it stays dark/black |
Conclusion: a shadow needs a light source, an opaque object, and a screen. Its shape, size, and sharpness depend on the object’s position relative to the light source and the screen, and changing the object’s colour never changes the shadow’s colour.
When the opaque object was a shiny object like a polished steel plate, I got a shadow on the screen, but I also saw that there was a bright spot of light on the wall on the opposite side. Why was it so?
A shiny, polished surface doesn’t just block light like a normal opaque object — it also changes the direction of light falling on it and sends it off elsewhere as a bright spot. This change in direction of light by a shiny surface or mirror is called the reflection of light.
Place the mirror in the path of the light beam passing through the slit, while keeping the comb steady. What do you observe? Also — in a mirror, I can see my face. Is that also due to reflection of light?
Fig 11.9a — A light beam
Fig 11.9b — Reflection in a mirrorThe straight path of the light beam changes direction the moment it falls on the mirror — this bending of the beam’s path is the reflection of light occurring at the mirror’s surface.
Yes — seeing your face in a mirror is also due to reflection of light: light from your face falls on the mirror, gets reflected, and reaches your eyes, letting you see your own image.
Compare the size of the pen’s image at different positions, check if it’s upright, try to catch it on a screen, and notice how far the image appears from the mirror when you stand at different distances. Also — which arm does your image raise when you raise your left arm?
Fig 11.10 — Image of a pen
Fig 11.11 — One’s own image- The image is exactly the same size as the object (the pen), no matter where it is placed in front of the mirror.
- The image is always erect (upright) — the tip of the pen stays on top at every position.
- The image cannot be obtained on a screen, placed either in front of or behind the mirror — it is a virtual image.
- The image appears to be exactly as far behind the mirror as the object is in front of it — move closer, and the image appears closer too.
- Raising your left arm makes your image raise its right-looking arm (and vice-versa) — your left appears as right in the mirror. This left-right reversal is called lateral inversion.
This is exactly why the word “AMBULANCE” is printed mirror-reversed on the front of an ambulance — it reads correctly when seen in the rear-view mirror of the vehicle ahead.
What do you see on the screen when light from a candle flame passes through a pinhole? Do you notice anything surprising? Are the images seen in a sliding pinhole camera erect or upside down?
Fig 11.12a — Simple pinhole setup
Fig 11.12b — Inverted flame image
Fig 11.13a — Pinhole box
Fig 11.13b — Screen box
Fig 11.13c — Sliding cameraLight from the candle flame travels in straight lines through the tiny pinhole and forms a real image of the flame on the screen — and yes, something surprising happens: the image is upside down (inverted).
In the sliding pinhole camera used outdoors, the image formed on the tracing-paper screen shows the true colours of the distant object, but it too always appears inverted — this is a basic property of every pinhole camera.
How does a periscope let us see objects that are not visible directly, and why does a kaleidoscope show a different pattern every time it is turned?
Fig 11.15a
Fig 11.15b
Fig 11.15c
Fig 11.15d — Pattern- Periscope: two plane mirrors fixed at 45° inside a Z-shaped box reflect light twice — once down each bend — letting the eye at the bottom see objects that are otherwise blocked from direct view (used in submarines, tanks, and bunkers).
- Kaleidoscope: three mirror strips joined in a triangle create repeated reflections of reflections of the coloured beads inside. Since there are 3 mirrors producing multiple overlapping images, a symmetric pattern forms — and because the loose beads shift every time the tube is turned, a new pattern appears each time.
Let Us Enhance Our Learning
All 12 end-of-chapter questions, solved step by step with clear reasoning for every match, MCQ, and figure-based question.
Which of the following are luminous objects? Mars, Moon, Pole Star, Sun, Venus, Mirror
A luminous object emits its own light, while a non-luminous object only reflects light falling on it.
- Luminous: the Sun (a star, emits its own light) and the Pole Star (also a star).
- Non-luminous: Mars, Moon, Venus, and Mirror — none of these emit their own light; they are visible only because they reflect sunlight (or other light) falling on them.
Match the items in Column A with those in Column B.
| 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 |
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.
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?
Light travels only in a straight line, so it can reach the eye only through a pipe segment that runs in an unbroken straight line all the way to the candle flame. Any bend in the pipe blocks the light from getting through.
Only Rekha can see the candle flame, because her branch of the pipe lies exactly in a straight line with the candle. Sahil, Patrick, and Qasima’s branches bend at the junction, so light cannot travel around the bend to reach their eyes.
Look at the images shown in Fig. 11.17 and select the correct image showing the shadow formation of the boy.
Since light travels in a straight line, a shadow always forms on the side of the object opposite to the light source (the Sun), touching the object at its base, with its length and direction matching the Sun’s position in the sky.
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.
- Scenario (i) — ball closer to the torch: the light rays from the torch are still spreading outward when they reach the ball, so it blocks a wider cone of light — the shadow on the wall is larger and more blurred.
- Scenario (ii) — ball closer to the wall: the ball is now nearer to the screen than to the source, so the shadow it casts is close to the ball’s actual size — the shadow is smaller and sharper.
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 | 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 on the left side of the ball | Two shadows would appear on the screen |
Torch close to ball → larger shadow; torch far away → smaller shadow; ball removed → bright spot on screen (nothing blocks the light); two torches on one side → two separate shadows (one cast by each source).
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.
A pinhole camera always forms a real, inverted image of the object, because light rays from the top and bottom of the object cross over at the tiny pinhole before reaching the screen.
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.
When held facing a plane mirror, your name appears left-right reversed in the image — letters look flipped horizontally, and the whole word may even look unreadable at a glance (mirror writing).
Reason: a plane mirror produces lateral inversion — it swaps left and right in the image while keeping up and down the same, so anything written on the paper is seen reversed left-to-right in the mirror.
Measure the length of your shadow at 9 AM, 12 PM, and 4 PM with the help of your friend. (i) At which of the given times is your shadow the shortest? (ii) Why do you think this happens?
- (i) The shadow is shortest at 12 PM (noon).
- (ii) At noon, the Sun is at its highest point in the sky, almost overhead, so sunlight falls on you at a very steep angle (close to vertical). This makes your shadow shrink to its shortest length. In the morning (9 AM) and afternoon (4 PM), the Sun is lower in the sky, so light falls at a slanting angle and casts a longer shadow.
On the basis of the 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
- Statement A is true — every image formed by a plane mirror undergoes lateral inversion (left and right are swapped).
- Statement B is also true — the letters T and O are both left-right symmetric shapes, so even after lateral inversion, their mirror images look exactly like the original letters.
Suppose you are given a tube of the shape shown in 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.
Yes, this tube can be used to make a periscope. Since the tube bends twice (like the Z-shaped periscope box), a plane mirror should be fixed at each bend, tilted at 45° to the tube’s axis, with both mirrors facing each other. Light entering from the top reflects off the first mirror, travels down the tube, reflects off the second mirror, and reaches the eye at the bottom — exactly like the periscope in Fig. 11.14.
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.
The shape, size, and sharpness of a shadow depend on how far the object is from the screen (here, the ground) relative to the light source (the Sun).
- When the bird flies high in the sky, it is very far from the ground, so the shadow it casts spreads out over a large area, becoming very large, faint, and blurred — too diffuse to notice.
- When the bird flies close to the ground, it is near the screen (ground), so its shadow stays small, sharp, and dark enough to be clearly visible.
@EDUGROWN — NCERT Curiosity Grade 7 · Chapter 11 Solutions