11.1 Sources of Light
1 · Does the Moon actually produce its own light?
No. The Moon is non-luminous; it merely reflects sunlight.
2 · Which objects give off their own light?
Any luminous object: the Sun, stars, lightning, flames, LEDs, fireflies, some deep-sea animals, etc.
11.2 Does Light Travel in a Straight Line? (Activities 11.1 & 11.2)
Activity 11.1 (match-box holes)
3 · Are you able to obtain the light spot on the screen after one box is shifted out of line?
No. The spot disappears because the three holes are no longer collinear; light cannot bend round the displaced box, proving it was travelling in a straight line.
Activity 11.2 (straight vs. bent pipe)
4 · Can you still see the candle flame through a bent pipe?
No. The flame is visible only when the pipe is perfectly straight. Bending the pipe blocks the straight-line path of light.
11.3 Light through Transparent, Translucent and Opaque Materials (Activity 11.3)
5 · Was your observation the same as your prediction? What can you conclude?
Observations match predictions:
| Material type | What happens | Conclusion |
|---|---|---|
| Transparent | Spot remains bright | Light passes almost completely |
| Translucent | Spot becomes faint | Light passes partially |
| Opaque | Spot vanishes; shadow forms | Light is blocked |
So: transparent → nearly all light passes; translucent → some; opaque → none.
11.4 Shadow Formation (Activity 11.4)
6 · Did a shadow form in every case?
Only when an opaque object blocked the beam. With no object, or with the torch switched off, no shadow appears.
7 · Does changing the colour of the object change the colour of the shadow?
No. The shadow of an opaque object is always dark regardless of the object’s colour.
8 · What factors affect shape, size and sharpness of a shadow?
Relative positions of light source, object and screen:
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Object closer to screen → smaller, sharper shadow.
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Object closer to light → larger, fuzzier shadow.
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Tilting the object tilts the shadow.
Removing screen, object or light removes the shadow entirely.
11.5 Reflection of Light (Activities 11.5 & 11.6)
Activity 11.5 (sunlight on mirror)
9 · Why do you see a bright spot of light on a wall that is not directly lit by the Sun?
Because the flat shiny plate (or mirror) reflects the sunlight, changing its direction and sending it to the wall.
Activity 11.6 (torch, comb, mirror)
10 · What happens to the thin beam of light after it strikes the mirror?
Its direction changes; you can trace a new straight-line beam emerging from the mirror. This confirms reflection by a plane mirror.
11.6 Images Formed in a Plane Mirror (Activities 11.7 & 11.8)
Activity 11.7 (pen and mirror)
11 · Are the object and its mirror image the same size?
Yes. A plane-mirror image is exactly the same size as its object.
12 · Is the image erect or inverted?
Erect (upright).
13 · Can the mirror image be obtained on a screen?
No. A plane-mirror image is virtual; it cannot be projected onto a screen.
Activity 11.8 (observer and mirror)
14 · How far behind the mirror does the image appear?
Exactly as far behind the mirror as the object is in front. If you stand 50 cm from the mirror, your image appears 50 cm behind the glass.
15 · What happens when you raise your left arm?
Your image appears to raise its right arm and vice-versa, an effect called lateral inversion.
11.7 Pinhole Camera (Activities 11.9 & 11.10)
Activity 11.9 (cardboard + candle)
16 · What do you see on the screen?
An inverted (upside-down) bright image of the candle flame.
Activity 11.10 (sliding pinhole camera)
17 · Do the images show colours?
Yes; a pinhole camera preserves the colours of the scene.
18 · Are the images erect or inverted?
Inverted.
11.8 Making Some Useful Items
No questions here—procedures only.
“LET US ENHANCE OUR LEARNING” (Blue-boxed Exercises)
**1 · Which of the following are luminous objects?
Mars, Moon, Pole Star, Sun, Venus, Mirror**
Answer: Only the Pole Star and the Sun are luminous. Mars, Moon, Venus and a mirror are non-luminous.
2 · Match Column A with Column B.
| Column A | Column B (matched item) |
|---|---|
| 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 |
3 · Who can see the candle flame in Fig 11.16?
Only Sahil looks straight through the un-bent pipe; Rekha, Qasima, and Patrick have bends, so they cannot see the flame.
4 · Select the correct image showing the boy’s shadow (Fig 11.17).
Image (a) — the shadow must lie directly opposite the light source and match the boy’s outline.
5 · Ball-and-torch shadow question (Fig 11.18).
Choose the correct representation of shadows for scenarios (i) and (ii).
Correct option: (b)
In (i) the ball is near the torch → large shadow; in (ii) near the wall → small shadow.
6 · Match torch position (Column A) with shadow characteristic (Column B).
| Column A | Column B |
|---|---|
| Torch close to ball | Shadow would be larger |
| Torch far from ball | Shadow would be smaller |
| Ball removed | A bright spot (no shadow) appears on screen |
| Two torches placed | Two shadows appear on screen |
(Note: the table given in the book had mismatched hints; the correct scientific mapping is above.)
7 · Sketch the outline of the tree’s image in a pinhole camera (Fig 11.19).
The drawn image should be upside-down and smaller, preserving the exact outline of the tree.
8 · Write your name on paper, hold it parallel to a plane mirror, and sketch the image. What difference do you notice? Explain.
Every letter appears laterally inverted (left-right reversed). Therefore, the whole word reads in reverse order, because a plane mirror swaps left and right.
**9 · Length of your shadow at 9 AM, 12 PM and 4 PM.
(i) At which time is the shadow shortest?**
At 12 PM (solar noon) when the Sun is highest.
(ii) Why?
Because the angle of sunlight is steepest; a higher Sun casts a shorter shadow.
10 · Statement-based MCQ
Statement A: Plane-mirror image is laterally inverted.
Statement B: Images of letters T and O appear identical to themselves.
Correct option: (iii) – Statement A is true; Statement B is false (letter T shows inversion, and letter O looks the same because of its symmetry).
11 · Can the angled tube (Fig 11.20) be used as a periscope? If yes, mark mirror positions.
Yes. Fix two plane mirrors at 45 ° inside each elbow so their reflecting faces are parallel and facing each other. Light enters the top opening, reflects down, then reflects again toward the viewer’s eye at the bottom opening.
12 · Why don’t we see a bird’s shadow on the ground when it is high in the sky, but we do when it swoops near the ground?
Far overhead, the bird is too small relative to its distance, so the umbra (full dark shadow) misses the ground and only a huge faint penumbra forms, which is imperceptible. Near the ground the umbra reaches the surface, producing a sharp visible shadow.
Exploratory Project Questions (Guidance)
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Firefly decline: Ask elders; likely causes are artificial lighting, pesticide use, habitat loss.
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Coloured torch paper: The shadow itself stays dark; only the lit background appears coloured.
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Mirrors at angles: Two mirrors at 90 ° show multiple images; parallel mirrors give an infinite series.
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Small mirror, large object: Yes; even a tiny plane mirror can show a full view (just limited field), proving mirror size doesn’t limit image size—only the aperture does.