Class 7 Science Chapter 11 Light, Shadows and Reflections Question Answer | NCERT Solutions

 

Science Class 7 Chapter 11 Question Answer Light Shadows and Reflections

Light Shadows and Reflections Class 7 Question Answer (InText)

Question 1.

What happens when an opaque object blocks the path of light? (Page 157)

Answer:

When light falls on an opaque object, it cannot pass through, and a dark region called a shadow appears on the screen or surface behind the object.

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? (Page 159)

Answer:

An opaque object with a polished surface, like a shiny plate, causes a bright spot due to the reflection of light.

Question 3.

In a mirror, I can also see my face. Is that also due to the reflection of light? (Page 160)

Answer:

Yes, we can see our face in a mirror due to the reflection of light.

Question 4.

Oh! Now I realise why  is written on an ambulance. It reads ‘AMBULANCE’ when viewed from the rear-view mirrors of the vehicle ahead of the ambulance. (Page 162)

Answer:

The word ‘AMBULANCE’ is written in an inverted (mirror) form on the front of an ambulance so that it appears correctly when seen in the rear-view mirror of a vehicle. This happens due to lateral inversion caused by the mirror.

Question 5.

Can we see an image of an object only in a mirror or are there some other ways as well? (Page 162)

Answer:

We can see an image of an object on a screen, through transparent materials, or in devices like a pinhole camera.

NCERT Class 7 Science Chapter 11 Question Answer Light Shadows and Reflections (Exercise)

Let Us Enhance Our Learning

Question 1.

Which of the following are luminous objects?

Mars, Moon, Pole Star, Sun, Venus, Mirror

Answer:

Sun (luminous because it produces its own light) Pole Star (luminous because it produces its own light) Venus, Mars, Moon and mirror all are non- luminous objects as they do not emit their own light.

Question 2.

Match the items in Column A with those in Column B.

Column A	Column B
(i) Pinhole	(a) Blocks light completely camera
(ii) Opaque object	(b) The dark region formed behind the object
(iii) Transparent object	(c) Forms an inverted image
(iv) Shadow	(d) Light passes almost completely through it

Answer:

Column A	Column B
(i) Pinhole	(c) Forms an inverted image
(ii) Opaque object	(a) Blocks light completely camera
(iii) Transparent object	(d) Light passes almost completely through it
(iv) Shadow	(b) 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. 11.16. Who can see the flame?

Answer:

Only Rekha can see the flame of the candle because light travels in a straight line, and Rekha’s line of sight is aligned with the flame. The others cannot see the flame because they are not in the path of the pipe where the flame is visible

Question 4.

Look at the images shown in Fig. 11.17 and select the correct image showing the shadow formation of the boy.

Answer:

The boy’s shadow is formed based on the light source. If the light is coming from above, the shadow will fall below. If the light comes from the side, the shadow will be cast in the opposite direction. Thus, option (d) is the correct image showing the shadow formation of the boy.

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. 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).

Answer:

In scenario (i), the ball is closer to the torch and away from the wall, so the shadow would be large and blurry on the wall. So the correct representation of scenario (i) will be (b). In scenario (ii), the ball is closer to the wall and away from the torch, so the shadow would be sharp and small. So the correct representation of scenario (ii) will be (a).

Question 6.

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.

Column A	Column B
(i) If the torch is close to the ball	(a) The shadow would be smaller
(ii) If the torch is far away	(b) The shadow would be larger
(iii) If the ball is removed from the set-up	(c) Two shadows would appear on the screen
(iv) If two torches are present in the set-up on the left side of the ball	(d) A bright spot would appear on the screen

Answer:

Column A	Column B
(i) If the torch is close to the ball	(b) The shadow would be larger
(ii) If the torch is far away	(a) The shadow would be smaller
(iii) If the ball is removed from the set-up	(d) A bright spot would appear on the screen
(iv) If two torches are present in the set-up on the left side of the ball	(c) Two shadows would appear on the screen

Question 7.

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.

Answer:

The formation of image of the tree formed in the pinhole camera is shown.

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.

Answer:

When you look at the paper through the plane mirror, the image will be laterally inverted (flipped horizontally). You will notice that the letters of your name appear backward, as the mirror reverses left and right.

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?

Answer:

(i) The shadow will be shortest at 12 PM when the Sun is directly overhead.

(ii) This happens because, at 12 PM, the Sun is at its highest point in the sky, so the angle between the Sun and the ground is almost 90 degrees, casting a shorter 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

Answer:

(i) Both statements are true. Plane mirrors create a laterally inverted image (left to right is reversed), and some alphabets like T and O appear the same in a plane mirror.

Question 11.

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.

Answer:

Yes, the tube can be used to make a periscope. The mirrors should be placed at a 45° angle inside the tube, facing each other, to reflect light through the tube and give you a view from above or around an obstacle.

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.

Answer:

This happens because the Sun’s rays are coming from a high angle when the bird is flying high, making the shadow very small and hard to notice. When the bird is closer to the ground, the angle of the sunlight creates a larger, more noticeable shadow on the ground.

Class 7 Light Shadows and Reflections Question Answer (Activities)

Activity 11.1: Let Us Investigate (Page 155)

Fig. 11.4: Matchbox activity light through holes

Observation and conclusion: When all three matchboxes are placed in a straight line, with holes at the same height and properly aligned, the light from the torch passes through all the holes and a bright spot appears on the screen placed on the opposite side. This proves that light travels in a straight line. However, when the holes are not in a straight line, the light cannot pass through, and no spot is seen on the screen.

Activity 11.2: Let Us Explore (Page 155)

Fig. Viewing candle flame through, (a) a straight pipe (b) a bent pipe

Observation and conclusion: We are able to see the candle flame through a straight pipe, as shown in fig. 11.5 (a), but not through a bent pipe, as shown in fig. 11.5 (b), because light travels in a straight line.

Activity 11.3: Let Us Experiment (pages 156-157)

Fig. Passing light through different materials

Table 11.1: Light through different materials

Material Cardboard	Transparent/ Translucent/Opaque	Light will pass fully/partially/not at all
		My prediction	My observation
Paper	Opaque	Not at all	Not at all
Glass	Opaque	Not at all	Not at all
Tracing	Transparent	Fully	Fully
paper	Translucent	Partially	Partially
Thick cloth	Opaque	Not at all	Not at all
Wax paper	Translucent	Partially	Partially
Water	Transparent	Fully	Fully

Observation and conclusion: Transparent materials allow light to pass through them completely, so we can see clearly through them. Translucent materials allow some light to pass through them, so we can see partially through them. Opaque materials do not allow light to pass through them, so we cannot see through them.

Activity 11.4: Let Us Explore (Pages 158-159)

Table 11.2: Observation of shadows

Action	Observations regarding shadow
The screen is removed.	Shadow cannot be seen
The object is removed.	No shadow is formed
The torch is switched off.	No shadow is formed
The object is moved closer to the screen, keeping the torch and the screen fixed.	Shadow becomes smaller
The object is moved closer to the torch, keeping the torch and the screen fixed.	Shadow becomes larger
The object is tilted, keeping the torch and the screen fixed.	Shape of shadow changes
The colour of the object is changed.	Colour of shadow does not change

Observation and conclusion: A shadow is formed when an opaque object blocks the path of light. The source of light, opaque object, and screen are necessary for the formation of a shadow. Changing the colour of the object does not affect the colour of the shadow. The position of the object affects the size and shape of the shadow:

1. If the object is moved closer to the screen, the shadow becomes smaller.
2. If the object is moved closer to the light source, the shadow becomes larger.
3. Tilting the object changes, the shape of the shadow.

Activity 11.5: Let Us Investigate (Pages 159-160)

Fig. Using mirror to redirect sunlight on a wall.

Observation and conclusion: When a shiny flat steel plate or mirror is tilted in different directions, we can see a spot of light on the wall or a nearby surface.

When we change the angle of the mirror or plate, the direction of the light also changes. This happens because the shiny surface or mirror changes the direction of the light that falls on it and this change in the direction of light by the mirror or shiny surface is known as reflection of light.

Activity 11.6: Let Us Experiment (Page 160)

Fig. (a) A light beam (b) Reflection of light in a plane mirror.

Observation and conclusion: When a narrow beam of light passes through a small slit and falls on a white sheet, it travels in a straight path, as shown in Fig.(a). However, when a plane mirror is placed in the path of this light beam, the direction of the beam changes, as shown in Fig. (b). This change in the direction of light when it strikes a shiny surface like a mirror is called reflection of light.

Activity 11.7: Let Us Experiment (Page 161)

Fig. Image of a pen in a plane mirror.

Observation and conclusion: In the plane mirror, image is formed behind the mirror and is of the same size as the object. The image formed by a plane mirror is always erect (upright) in nature. However, the image formed by a plane mirror cannot be obtained on the screen.

Activity 11.8: Let Us Experiment (Pages 161-162)

Fig. Observing one’s own image in a mirror.

Observation and conclusion: In a plane mirror, the image is formed at the same distance behind the mirror as the object is in front of it. If the object is closer to the mirror, the image will also be closer. If the object is far from the mirror, the image will also appear far. In a plane mirror, the right appears as left and left appears as right; this is due to lateral inversion.

Activity 11.9: Let Us Explore (Page 163)

Fig. (a) A simple pinhole camera (b) Image of a candle flame on screen.

Observation and conclusion: When we place a lighted candle in the front of a cardboard with a small hole, as shown in fig. (a), the light coming from the flame passes through the hole and forms an inverted (upside-down) image of a candle on the screen behind the cardboard, as shown in fig. (b).