STD 10 Physics: Chapter 04 Reflection of Light - Questions and Answers
Class 10 Physics Chapter 03 Reflection of Light
Reflection of Light - TextBooks Questions
1. What is light?
Light is a form of energy essentially required to see objects.
2. Observe the figure.
b. Which is the reflected ray?
c. Is there any relation between the angle of incidence and the angle of reflection?
d. Are the incident ray, reflected ray and normal to the mirror at the point of incidence in the different planes?
Answer:
a. AO
b. QB
c. The angle of incidence and angle of reflection are equal.
d. In the same plane
3. Let's Write down the laws of reflection?
- When light is reflected from a smooth surface, the angle of incidence and angle of reflection are equal.
- The incident ray, reflected ray and normal to the surface area in the same plane.
4. A beam of light incident on two surfaces with different properties is depicted below.
Answer: In the first figure the surface is smooth, in the second figure surface is rough.
b. Fig. 4.2(b) are the rays of light travelling parallel after reflection?
Answer: No. When light falls on a rough surface, it undergoes an irregular reflection. This is a scattered reflection.
c. In Fig. 4.2(a) regular reflection is depicted. Can you give a definition for such reflections by observing the figure?
Answer: When light falls on a smooth surface, it undergoes a regular reflection, the rays of light travelling parallel after reflection This is regular reflection.
5. Record in your science diary the following features about the images formed here.
Answer: Equal
b. Is the image real or virtual?
Answer: Virtual
c. The size of the image.
Answer: Same size as object.
6. Arrange two plane mirrors in such a way that their edges are in contact as shown in the figure. Place a burning candle in between them. How many images of the candle can you see?
Answer: 3
b. What if viewed from other positions in between the mirrors?
Answer: 3
c. How much is the angle between the mirrors?
Answer: 90°
d. What is the relation between the angle between the mirrors and the number
Answer:
7. (a) Observe the table below. The Position of the image and the features of the image when objects are placed in different positions in front of different types of mirrors are tabulated.
(P) At focus, small, real, inverted
(Q) Between F and C, small, real, inverted
(R) At C same size as object, real, inverted
(S) Beyond C, big, real, inverted
(T) At infinity, no images
(U) At behind the mirror, very large, virtual, direct
(b) By Completing Table 4.2 and by analysing it, we can reach the following interferences. Can you write down some situations in daily life in which we can make use of the interferences?
8. What is the field of view?
- The field of view of a mirror is the maximum range of the vision through the mirror.
9. Why convex mirror is used as a rearview mirror?
- Large field of view
10. Arrange the materials as shown below and arrange the screen in front of the mirror so that you get a clear reflection of the candle.
b. Observe the change in position of image and features on changing the position of the candle
c. Consider u as the distance of the object from the mirror and v as the distance to the image from the mirror. Measure them and tabulate. Repeat the activity by changing the position of the object.
Answer:
a. Between F and C, small, real, inverted.
b. Depending on the position of the candle the position of the reflector receiving in the mirror also changes.
c. 
11. What is Mirror equation?
It is an equation relating object distance and image distance with focal length is known as a mirror equation. It is also known as a mirror formula.
- In all experiments related to lenses and mirrors the distances are measured in the same way as in graphs.
• Distances are measured considering the Pole of the mirror as the origin (O).
• Those measured to the right from O are positive and those in the opposite direction are negative.
• Distances measured upwards from X-axis are positive and those downwards are negative. The incident ray is to be considered as travelling from left to right.
13. Record the measurements shown in the figure using the New Cartesian Sign Convention.
b. Distance to the image from the mirror (v) = Negative.
c. Height of object (OB) = Positive.
d. Height of image (IM) = Negative.
14. The given figure shows the image formation by a concave mirror. Analyse the figure and write down different measures using New Cartesian Sign Convention.
(b) Is there any relationship between the position of the image and the size of the image. Complete the below table.
17. What are the features of an image that is obtained from magnification?
(a) Observe the given figures and complete the table using the New Cartesian Sign Convention.
(b) Analyse the table and mark the correct statements.
i. When magnification is 1, the size of the image and the size of the object are equal.
ii. When magnification is more than 1, the size of the image is greater than the size of the object.
iii. When magnification is less than 1, the size of the image is smaller than the size of the object.
iv. When the magnification is positive, the image is real and inverted.
v. When the magnification is negative, the image is virtual and erect.
Answer: (a)
ii. When magnification is more than 1, the size of the image is greater than the size of the object.✔
iii. When magnification is less than 1, the size of the image is smaller than the size of the object.✔
iv. When the magnification is positive, the image is real and inverted.✖
v. When the magnification is negative, the image is virtual and erect.✖
18. Write down two uses of the convex mirror.
(i) Used in vehicles as a rearview mirror
(ii) Used in street lights
19. Why convex mirror is used as a rearview mirror?
The viewing area of convex mirrors is very wide. Therefore, the size of the reflection of an object allows the mirror to capture more of its surroundings. It is widely used in vehicles as it allows the driver to sense the traffic behind the vehicle very quickly.
20. Why it is written on rearview mirrors that “Objects in the mirror are closer than they appear”.
- The image formed by a convex mirror is always erect and diminished. Hence the driver who sees the image of vehicles on the mirror develops a feeling that the vehicles coming from behind are at a greater distance. This may turn out to be dangerous.
21. Which mirror have least field of view?
- Concave mirror
22. An object is placed 30cm away from a spherical mirror. Its magnification is found to be -1.
a) Write the peculiarities of the image.
b) Which mirror is used here?
c) If the object is placed 10cm away from the mirror, what change will occur to the nature of the image formed?
d) Justify your conclusions.
Answer:
a) Real inverted, same size of the object.
b) Concave mirror
c) Image is erect, Virtual and diminished.
d) Since the magnification is one object is at C. So r = 30cm, f = 15cm
If the object is 20cm away, it will be between f and P. So an erect, large, real image will be formed on the other side of the mirror. 23. Image is not visible on a rough wooden block. But when the surface is polished an image can be seen. Why?
Hints: Irregular reflection occurs on a rough surface. So no image can be seen. On a polished surface regular reflection takes place. So the image is visible.
Hints: Irregular reflection occurs on a rough surface. So no image can be seen. On a polished surface regular reflection takes place. So the image is visible.
24. If the height of the image is given with negative sign as per new cartesian sign convention, what all peculiarities of an object can be identified?
- Real and inverted image
- Real and inverted image
25. What are the peculiarities of the image formed by a plane mirror?
- Virtual, Erect, Same size
26. Which mirror forms an erect and diminished image?
- In a convex mirror
- In a convex mirror
27. Which mirror forms an erect and large image?
- concave mirror
- concave mirror
28. Observe the diagram and complete the following using new cartesian sign convention.
a) Height of image .......................
b) Height of object ..........................
c) Distance from the pole to the object .....................
d) Distance from the pole to the image ....................
Answer:
a) – 2 cm
b) 5 cm
c) – 100 cm
d) – 30 cm
29. Vijay and Kiran form the image of an object on the screen using a concave mirror of focal length 40cm.
a) Vijay places the object at a distance of 80cm and conduct the experiment. How far the screen be placed to get a clear image?
b) Kiran places the object at a distance of 10cm and conduct the experiment. Then how far the screen be placed to get a clear image?
a)Screen must be placed 80cm away from the pole of the mirror.
b) Screen must be placed 60cm away from the pole of the mirror.
Answer:
a) Vijay
f = -40cm
u = -80cm
v = ?
1/v+1/u =1/f
1/v = 1/f-1/u
1/v = 1/-40 - 1/-80
= -80cm
screen should be placed 80cm away from the pole of the mirror.
(b) കിരൺ
f = -40cm
u = -120cm
v = ?
1/v+1/u =1/f
1/v = 1/f-1/u
1/v = 1/-40 - 1/-120
= -60cm
30. Why plane mirrors are used to see the image of face?
- Erect, same size images are formed.
31. Radha used three mirrors to look at her face. She found the size of the image different on three occasions. Identify the mirrors by understanding the difference in the size of image formed.
a) Image of face is big.
b) Image of face is small
c) Image of same size
Answer:
a) Concave mirror
b) Convex mirror
c) Plane mirror
32. What will be the nature of the image when the magnification is positive in mirrors.
- Virtual and erect
33. Find out the true statements from the following.
a) When the magnification is greater than one, the size of the image is less than object.
b) When the magnification is greater than one. The size of the image is greater than object.
c) When the magnification is positive, image will be real and inverted.
d) When the magnification is negative, image will be virtual and inverted.
Answer:
b)When the magnification is greater than one the size of the image will be greater than object.34. An object of height 10cm is placed at a distance of 50cm from a concave mirror. Focal length of the mirror is 20cm. Which among the following could be the height of image?
(+10cm, -10cm, +7cm, -7cm)
Answer: -735. Concave mirrors are used to construct solar furnaces. Convex mirrors are not used. Why?
- Light rays and heat rays coming parallel to the principal axis converges on a point on the principal axis in concave mirrors, the convergence of heat radiations are used in solar furnace for heating.
But in convex mirrors rays coming parallel to the principal axis are diverging after reflection, not converging. So can not be used for constructing solar furnaces.Evaluation questions
Let us assess
1. A dental doctor uses a mirror of focal length 8 cm. To see the teeth clearly what should be the maximum distance between the teeth and the mirror? Justify your answer. Which type of mirror has been used by the doctor?
- The dental doctor uses a concave mirror. Effect and enlarged image can be obtained using the mirror. Such images are formed when the object is kept in between the main focus and pole of a concave mirror. So the minimum distance between the mirror and the teeth must be in 8 cm to view the teeth clearly.
- The dental doctor uses a concave mirror. Effect and enlarged image can be obtained using the mirror. Such images are formed when the object is kept in between the main focus and pole of a concave mirror. So the minimum distance between the mirror and the teeth must be in 8 cm to view the teeth clearly.
2. Imagine that a spherical mirror gives an image magnified 5 times at a distance of 5 m. If so determine whether the mirror is concave or convex. How much will be the focal length of the mirror?
- Given that the object is after, the reflection is real and therefore the concave mirror.
u = 5u+5
5 = 5u-u, 5 = 4u, u = 5/4 = 1.25cm
from the equation v=u+5,
u =1.25m
then v = 1.25 m + 5 = 6.5m
3. A motorcyclist observes a car coining from behind with a magnification 1/6. If the actual distance between the car and the bike is 30 m calculate the radius of curvature of the mirror.
R=2f
R=2X6=12m
4. A shaving mirror of focal length 72 cm is kept in a beauty clinic. A man uses it standing 18 cm away from the mirror. At what distance will the image be formed? Is the image real or virtual? What is the magnification of the image?
- This is a concave mirror.
5. Wrap a rubber ball of diameter 12 cm completely with an aluminium foil and make the surfaces smooth. Where will be the image of an object kept 12 cm away from the centre of the ball? Is the image real or virtual?
- assume that the inner part of the ball is covered with aluminium foil then it becomes a concave mirror.
diameter = -12 cm,
R = 6 cm
6. We are able to read a book since light falling on a surface gets reflected from the book and reaches the eye. But on such occasions, we cannot see our images like that from a mirror. Explain why?
- Irregular reflection takes place in the book. So images not formed.
7. Is the image formed by a plane mirror real or virtual? Write an instance when such a mirror gives an inverted image.
- Image formed by a plane mirror is always direct and virtual. The image will be at the same distance at the object.
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