11. Light: Shadows and Reflections
Complete solutions to Let Us Enhance Our Learning. CBSE / NCERT Class 7 Science (Curiosity).
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Let Us Enhance Our Learning
Luminous objects: Pole Star Sun
They give out their own light. Mars, Moon and Venus only reflect the light of the Sun. A mirror only reflects light.
| 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 |
Rekha can see the flame.
Light travels in a straight line. Only Rekha’s pipe is straight from the candle to her eye. The other pipes are bent.
Correct image: (d)
A shadow is always formed on the side opposite to the source of light. In (d), the Sun is towards the right, and the shadow falls towards the left.
- Scenario (i), ball near the torch: (b) — larger shadow.
- Scenario (ii), ball near the wall: (a) — smaller shadow.
When the object is closer to the source of light, it blocks more light. So the shadow is larger.
| 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 |
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A pinhole camera forms an inverted (upside-down) image. The trunk appears at the top and the leafy top appears at the bottom.
The image of the tree in a pinhole camera is upside down.
Example: the name RAVI and its image in a plane mirror.
The letters appear reversed from left to right. The name reads backwards in the mirror.
This happens because the image formed by a plane mirror is laterally inverted. The left side of the object appears as the right side in the image, and the right side appears as the left.
(i) The shadow is shortest at 12 PM (noon).
(ii) At noon, the Sun is almost overhead. Light falls nearly straight down on us, so the shadow is short. In the morning and evening, the Sun is low in the sky. Light falls at a slant, so the shadow is long.
Answer: (i) Both statements are true
T and O are the same on their left and right sides. So even after lateral inversion, their images look the same.
Yes, it can be used to make a periscope.
Fix one mirror at each bend (corner) of the tube. Each mirror should be at an angle of 45°, and the two mirrors should face each other.
Position of the two plane mirrors in the tube.
Light entering the top opening is reflected down by Mirror 1. Mirror 2 reflects it out through the lower opening to the eye.
- The bird is very small compared to the Sun, which is a very big source of light.
- When the bird is high up, light from different parts of the Sun reaches the ground around the bird from all sides. The shadow becomes very faint and is not seen.
- When the bird comes near the ground, it blocks light from reaching a small area just below it. So a clear, dark shadow is formed.
Exploratory Projects
Exploratory Projects are hands-on tasks. Do them with your classmates under the guidance of your teacher, and write your own observations.