Light: Shadows and Reflections — Complete Solutions
Step-by-step answers to every in-text activity and every question from “Let Us Enhance Our Learning,” with clear diagrams for straight-line light, shadows, mirrors, and the pinhole camera.
In-text Questions & Activities
Solutions for every activity, “Dive Deeper” box, and embedded question that appears inside the chapter, in the order they appear.
No. Once even one hole is out of line with the other two, the light spot disappears from the screen.
Conclusion: This observation shows that light travels in a straight line — light from the torch can only pass through all three holes and reach the screen when they are exactly aligned.
You can see the candle flame through the straight pipe, but not through the bent pipe.
Conclusion: Light rays from the flame cannot bend around the curve in the pipe, so they never reach your eye — this again shows that light travels in a straight line.
Yes. The milk particles scatter the laser light, making the beam visible as a glowing straight red line as it crosses the beaker — confirming that light travels in a straight line, even inside water.
| Material | Transparent / Translucent / Opaque | My prediction | My observation |
|---|---|---|---|
| Cardboard | Opaque | Not at all | Not at all |
| Paper | Translucent | Partially | Partially |
| Glass | Transparent | Fully | Fully |
| Tracing paper | Translucent | Partially | Partially |
| Thick cloth | Opaque | Not at all | Not at all |
| Plastic sheet (clear) | Transparent | Fully | Fully |
| Wooden board | Opaque | Not at all | Not at all |
| Action | Observation regarding shadow |
|---|---|
| The screen is removed. | No shadow can be observed — light just spreads into the surroundings without landing on any surface. |
| The object is removed. | No shadow forms — the full spot of light appears on the screen instead. |
| The torch is switched off. | No shadow forms, since there is no light to be blocked. |
| The object is moved closer to the screen, keeping the torch and screen fixed. | The shadow becomes smaller and sharper. |
| The object is moved closer to the torch, keeping the torch and screen fixed. | The shadow becomes larger and more blurred. |
| The object is tilted, keeping the torch and the screen fixed. | The shape/size of the shadow changes according to the new orientation of the object. |
| The colour of the object is changed. | The shadow’s colour does not change — it stays dark/black regardless of the object’s colour. |
Tilt or turn the mirror in different directions until the reflected sunlight lands on the desired wall. As you rotate the mirror, the bright spot of light on the wall moves too — showing that the mirror is changing the direction of the light that falls on it. This bending of light’s direction by a shiny/mirrored surface is called reflection of light.
The path of the light beam changes direction the moment it strikes the mirror. This confirms that reflection of light occurs at the mirror — the mirror redirects the beam along a new straight path.
- Size: The image of the pen is always the same size as the pen itself, no matter where you place it in front of the mirror.
- Orientation: The tip of the pen always appears on top — the image is erect (upright) at every position.
- Screen test: The image cannot be obtained on a screen placed either behind or in front of the mirror — it only appears to exist behind the mirror’s surface.
The image always appears to be exactly as far behind the mirror as you are standing in front of it — move closer, and the image moves closer too (by the same amount).
When you raise your left arm, your image appears to raise its right arm (as you view it). When you touch your right ear, the image appears to touch its left ear.
Light rays from the top and bottom of the flame travel in straight lines and cross over at the pinhole, so the image formed on the screen is upside down (inverted). When you build the sliding pinhole camera outdoors, the image of a tree or building also appears inverted, but shows the true colours of the object.
Exercise Questions — Let Us Enhance Our Learning
All 12 questions from the end-of-chapter exercise, answered in full with reasoning and diagrams.
Luminous (emit their own light): Sun Pole Star
Non-luminous (do not emit their own light — only reflect light falling on them): Mars, Moon, Venus, and Mirror.
| 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 |
Only the branch that forms one continuous straight line with the candle’s pipe lets light through.
Only Rekha can see the candle flame. Light travels in a straight line, and only Rekha’s section of the pipe forms one straight, unbroken line with the section leading to the candle. Sahil’s, Patrick’s, and Qasima’s pipes bend at the junction, so light from the flame cannot turn the corner to reach their eyes.
Sun upper-left → shadow falls away from the Sun, on the lower-right side of the boy — this matches option (d).
Option (d) is correct. A shadow always forms on the side of an object opposite to the light source. Since the Sun is shown in the upper corner of the picture, the boy’s shadow must stretch out on the ground on the far side, away from the Sun — exactly as shown in image (d).
(i) Ball close to torch → large, blurred shadow = option (b)
(ii) Ball close to wall → small, sharp shadow = option (a)
Scenario (i) — ball closer to the torch: the shadow is large and blurry (option b), because the ball blocks a wider spread of light rays close to the source.
Scenario (ii) — ball closer to the wall: the shadow is small and sharp (option a), close to the actual size of the ball.
| 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 |
Light rays from the top and bottom of the tree cross at the pinhole and swap places.
The image of the tree formed in the pinhole camera is an inverted (upside-down) outline of the same tree — the treetop points downward and the trunk points upward, because light rays travel in straight lines and cross over at the pinhole.
Your name (left) appears mirror-flipped (right) — letters reversed left-to-right.
The image of your name in the mirror appears laterally inverted — flipped left-to-right, so the letters read backward (like “RAHUL” becoming a mirror-flipped version that is hard to read normally). This happens because a plane mirror reverses left and right (though not up and down), a property called lateral inversion.
The shadow is shortest at 12 PM (noon).
At noon, the Sun is almost directly overhead, so light rays fall nearly straight down, producing a very short shadow. In the morning (9 AM) and afternoon (4 PM), the Sun is lower in the sky, so light rays fall at a slanting angle, casting long shadows.
Statement B: Images of alphabets T and O appear identical to themselves in a plane mirror. (i) Both true (ii) Both false (iii) A true, B false (iv) A false, B true
iBoth statements are true.✓ Correct option
- Statement A is true — every image formed by a plane mirror is laterally inverted (left–right reversed).
- Statement B is also true — letters T and O are both symmetric about a vertical line down their middle, so flipping them left-to-right leaves them looking exactly the same as the original.
Both mirrors go exactly at the two bends of the tube, each angled at 45° to the tube’s walls.
Yes, this tube can be used to make a periscope. Fix one plane mirror at each of the two bends in the tube, with each mirror tilted at 45° to the walls of the tube and facing the other mirror. Light entering the top opening reflects off the first mirror, travels down the tube, and reflects off the second mirror straight into your eye.
A shadow is technically formed at every height, but its visibility depends on how large, faint, and spread out it becomes:
- When the bird is flying high, it is very far from the ground (the screen). Its shadow spreads out over a much larger area and becomes extremely faint and blurred — too diffuse for our eyes to notice against the ground.
- When the bird swoops close to the ground, it is near the “screen,” so its shadow stays small, sharp, and dark — clearly visible.
Exploratory Projects — Quick Guidance
These are open-ended activities, not questions with one fixed answer — here’s how to approach each one.
Firefly investigation: Ask elders whether fireflies were more common in your area earlier. If yes, research causes for decline — light pollution, pesticide use, habitat/forest loss, and urbanisation — and turn your findings into a short story.
Coloured shadows: Cover the torch face with coloured transparent paper (red, blue, green) and repeat Activity 11.4. You’ll find the shadow itself stays dark/black, but the region around the shadow is tinted with the colour of the transparent paper, since only that colour of light passes through.
Two mirrors at an angle: Place two mirrors at an angle to each other (as in Fig. 11.21) with an object between them. As the angle decreases, the number of images increases — at 90° you get 3 images, and as the mirrors approach parallel, you get a near-endless tunnel of images (each a reflection of a reflection).
Small mirror, big tree: Yes — even a small plane mirror can form a complete image of a much larger object like a tree. Step back far enough from the mirror, and your eye can pick up reflected rays from the entire tree converging through that small mirror surface into your eye.