Solutions (Exercise + Intext)
Intext Questions :
Question 1. What happens when an opaque object blocks the path of light?
When an opaque object blocks the path of light, it creates a shadow. Since light travels in a straight line, it cannot pass through the opaque material, resulting in a dark patch on a surface or screen where the light is unable to reach.
Question 2 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 opaque object, like a polished steel plate, creates both a shadow and a bright spot because it interacts with light in two ways:
- Shadow formation: Because the object is opaque, it blocks the light from continuing forward, creating a dark region.
- Reflection: Because the surface is shiny and polished, it acts like a mirror and changes the direction of the light that falls on it. This redirected light creates the bright spot on the opposite wall, a process known as reflection of light.
Question 3 In a mirror, I can also see my face. Is that also due to the reflection of light?
Yes, seeing your face in a mirror is directly due to the reflection of light. What you observe is a reflection of your face being bounced back to your eyes by the mirror's surface.
Question 4 Can we see an image of an object only in a mirror or are there some other ways as well?
We can see images of objects in ways other than just mirrors.
For example,
- A pinhole camera can be used to form an image of an object on a screen. In a pinhole camera, light rays pass through a tiny hole and create an inverted (upside down) image of the object.
- Additionally, devices like periscopes use multiple reflections from mirrors to allow us to see objects that are not in our direct line of sight.
Let Us Enhance Our Learning : Exercise Questions
Question 1. Which of the following are luminous objects?
Mars, Moon, Pole Star, Sun, Venus, Mirror
Pole Star and Sun
Question 2. Match the items in Column A with those in Column B.
| Column A | Column B |
| Pinhole camera | Blocks light completely |
| Opaque object | The dark region formed behind the object |
| Transparent object | Forms an inverted image |
| Shadow | Light passes almost completely through it |
| 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 |
Question 3. Sahil, Rekha, Patrick, and Qasima are trying to observe the candle flame through the pipe as shown in Fig. Who can see the flame?
Rekha can see the flame
Question 4. Look at the images shown in below Fig. and select the correct image showing the shadow formation of the boy.
Correct image is (d)
- In the image, the sun is shown in the sky and shadows are always formed opposite to the direction of the light source.
- In option (d), the boy's shadow is correctly shown behind him and in the direction opposite to the sun.
Question 5. The shadow of a ball is formed on a wall by placing the ball in front of a fixed torch as shown in Fig. 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).
(i) If ball is closer to the torch, the shadow is larger (b).
(ii) If ball is closer to the wall, the shadow is smaller (a).
Question 6. Based on above Fig., 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 smaller |
| If the torch is far away | The shadow would be larger |
| If the ball is removed from the set-up | Two shadows would appear on the screen |
| If two torches are present in the set-up on the left side of the ball | A bright spot would appear on the screen |
| Column A (Torch Position/Action) | Column B (Shadow Characteristic) |
| 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 |
Question 7. Suppose you view the tree shown in Fig. through a pinhole camera. Sketch the outline of the image of the tree formed in the pinhole camera.
Question 8. 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.
Sketch of the Image: If you write "RAKESH" on a piece of paper and look at it in a plane mirror, the name will appear backwards. The letters will look reversed from left to right. (See above fig.)
Difference Noticed: The left side of the name appears on the right side in the mirror, and the right side appears on the left side. Therefore, the word looks reversed.
Reason:
This happens because of lateral inversion.
- A plane mirror swaps the left and right sides of an object.
- The image remains upright (erect) and is not upside down.
- Due to this left-right reversal, the name appears backwards in the mirror.
Question 9. 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?
Observations :
| Time | Length of Shadow |
| 9:00 AM | Long |
| 12:00 PM | Shortest |
| 4:00 PM | Long |
(i) The shadow is shortest at 12:00 PM (noon).
(ii) Why this happens : At noon, the Sun is almost directly overhead. Therefore, the sunlight falls nearly vertically on our body, producing the shortest shadow. In the morning and evening, the Sun is lower in the sky, so the shadows become longer.
The length of a shadow depends on the position of the Sun in the sky. The higher the Sun, the shorter the shadow.
Question 10. 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
(i) Both statements are true
Question 11. Suppose you are given a tube of the shape shown in the Fig. 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, the tube shown in Figure can be used to make a periscope.
- Fix one plane mirror at the top opening of the tube, tilted at a 45° angle to reflect incoming light downward.
- Fix the second plane mirror at the bottom opening, also tilted at a 45° angle to reflect the light towards the viewer's eye.
Question 12. 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.
- When a bird flies high in the sky, its shadow falls very far from the bird and becomes large, faint, and difficult to see on the ground.
- When the bird swoops near the ground, the shadow is formed closer to the bird. It becomes smaller, darker, and clearer, so we can easily see it.
- Therefore, we usually do not see the shadow of a bird flying high in the sky, but we can see it when the bird comes close to the ground.
We reply to valid query.