Light: Shadows and ReflectionsClass 7 Science NCERT Solutions
12 Solutions
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Solution 1 of 12
Q1Let Us Enhance Our Learning
Which of the following are luminous objects? Mars, Moon, Pole Star, Sun, Venus, Mirror
Solution
The luminous objects are Pole Star and Sun. Luminous objects are those that emit their own light. The Sun and stars generate light through nuclear reactions.
Q2Let Us Enhance Our Learning
Match the items in Column A with those in Column B.
\begin{tabular}{|l|l|}
\hline Column A & Column B
\hline Pinhole camera & Blocks light completely
\hline Opaque object & The dark region formed behind the object
\hline Transparent object & Forms an inverted image
\hline Shadow & Light passes almost completely through it
\hline
\end{tabular}
Solution
Here is the correct matching of items in Column A with 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
Q3Let Us Enhance Our Learning
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?
Solution
Sahil and Qasima can see the flame. Light travels in a straight line, so the person looking through a straight pipe will be able to see the flame. Rekha and Patrick are using a bent pipe, therefore they cannot see the flame.
Q4Let Us Enhance Our Learning
Look at the images shown in Fig. 11.17 and select the correct image showing the shadow formation of the boy.
Solution
The correct image showing the shadow formation of the boy is the one where the shadow is directly behind the boy and generally matches the shape of the boy. The shadow is formed because light is blocked by the opaque object (the boy).
Q5Let Us Enhance Our Learning
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 from the options provided ( a and b ).
Solution
In scenario (i), where the ball is closer to the torch, the shadow would be larger. In scenario (ii), where the ball is closer to the wall, the shadow would be smaller and sharper.
Q6Let Us Enhance Our Learning
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.
\begin{tabular}{|l|l|}
\hline Column A & Column B
\hline If the torch is close to the ball & The shadow would be smaller
\hline If the torch is far away & The shadow would be larger
\hline If the ball is removed from the set-up & Two shadows would appear on the screen
\hline If two torches are present in the set-up on the left side of the ball & A bright spot would appear on the screen
\hline
\end{tabular}
Solution
Here is the correct matching of items in Column A with 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 in the set-up on the left side of the ball: Two shadows would appear on the screen
Q7Let Us Enhance Our Learning
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.
Solution
The image of the tree formed in the pinhole camera will be inverted (upside down). The outline will show the shape of the tree, but with the top of the tree at the bottom and the roots at the top.
Q8Let Us Enhance Our Learning
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.
Solution
The image in the plane mirror will show lateral inversion. This means that the left side of your name will appear as the right side in the image, and vice versa. For example, if your name is 'RAM', the image will appear as 'MAR'. This happens because the mirror reflects the image, reversing it left to right.
Q9Let Us Enhance Our Learning
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?
Solution
(i)
The shadow is the shortest at 12 PM.
(ii)
At 12 PM, the Sun is almost directly overhead. When the Sun is directly overhead, the angle of incidence is such that the shadow length is minimized. As the sun gets lower in the sky, the shadow becomes longer.
Q10Let Us Enhance Our Learning
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
Solution
The correct option is (i) Both statements are true. Statement A is true because plane mirrors cause lateral inversion. Statement B is also true because the letters 'T' and 'O' are symmetrical and their images appear identical in a plane mirror.
Q11Let Us Enhance Our Learning
Suppose you are given a tube of the shape shown in the 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.
Solution
Yes, this tube can be used to make a periscope. The plane mirrors should be fixed at a 45-degree angle to the horizontal at each bend in the tube. This will allow light to reflect from one mirror to the other, enabling you to see around the corner.
Q12Let Us Enhance Our Learning
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.
Solution
When a bird is flying high in the sky, its shadow is very faint and spread out over a large area. This is because the light rays are diffused by the distance. Also, the shadow is not sharp due to the distance. However, when the bird swoops near the ground, the shadow becomes more defined and concentrated because the distance between the bird and the ground is reduced. The light rays are less diffused and the shadow is more easily visible.