a) To determine the focal length of the concave mirror three students 𝐴, 𝐵 and 𝐶 focused on a distance building on a screen. They measured the distance as given below: 

Student 𝐴: From the mirror to the screen 

Student 𝐵: From building to the screen 

Student 𝐶: From the building to the mirror

Who measured the focal length correctly?

 

A) Only A
B) Only B
C) A and B
D) B and C
 

 

                                                                                                             OR 

 

Study the following ray diagram:

Identify the angle of incidence, the angle of emergence and the angle of deviation respectively in the given diagram.

 

A) 𝑦, 𝑝 and z

B) 𝑥, 𝑞 and z

C) 𝑝, 𝑦 and z

D) 𝑝, 𝑧 and y

 

a) 

Option (a) is correct. 

● In a concave mirror, the focal length is the distance between the pole and the focus. 

● Student 𝐴 measured the focal length correctly. 

● Because he measured the length between the concave mirror and the screen. 

Option (b) is incorrect. 

● In option (b), it is given that the focal length measured by the student 𝐵 only is correct. 

● Student 𝐵 measures the distance from the building. 

Option (c) is incorrect. 

● In option (c), it is given that the focal length measured by students 𝐴 and 𝐵 is incorrect. 

● Focal length is the distance between the screen and the mirror in the concave mirror. ● So, the focal length measured by the student 𝐴 only is correct. 

● So, option (c) is incorrect. 

Option (d) is incorrect. 

● In option d, it is given that the focal length measured by students 𝐵 and 𝐶 is correct.

● Focal length is the distance between the screen and the mirror in a concave mirror. 

● So, the focal length measured by students 𝐵 and 𝐶 is incorrect. 

● So, option (d) is incorrect. 

Hence option (a) Student 𝐴: From the mirror to the screen is correct.

                                                                                          OR

b)

In this diagram, the angle of incidence, the angle of emergence and the angle of deviation, respectively, have been represented by 𝑝, 𝑦 and 𝑧. 

Let us discuss the terms angle of incidence, angle of emergence and angle of deviation:

The angle of incidence: The angle between the incident ray and the normal to the surface of the prism at which the ray of light is incident known as the angle of incidence. 

The above figure shows that the ray of light is entering the prism at an angle of 𝑝. So, the angle of incidence is 𝑝. 

The angle of emergence: The angle from where the ray is going out from the prism is called the angle of emergence. It is the angle formed between the ray of emergence and normal to the surface from where the ray is emerging. 

In the above figure, we note that the angle of emergence is 𝑦. 

So, the angle of emergence is 𝑦. 

The angle of deviation: The angle at which the ray has deviated from the incident angle. This angle is known as the angle of deviation. 

In the above figure, we see that the angle of deviation is given by 𝑧. 

Hence option (c) 𝑝, 𝑦 and 𝑧 is correct.