Question

what is angle of incidence of a ray if the angle between the incident and reflected rays is 120 degree?.......plz give ans with explanation.

Answer 1

If I understood your question, then I guess you want to ask the angle of Incidence for a ray of light on a plain reflecting surface, which is making an angle of 120° with the reflected light.

The answer is 30°.

Explanation: If we consider the surface is flat surface (ideal), then total angle is 180°. Then if the angle between the Incident Ray and Reflected Ray is 120° then we are left with (180° - 120°) = 60°. This 60° is equally divided between the Incident Ray and the Reflected to follow the Laws of Reflection. So, 60° / 2 = 30°.

#Cheers :)

Answer 2

Given:

The angle between incidence ray and reflected ray is 120°

To find:

Incident angle

Solution:

As we know according to the law of reflection, the angle of incidence is the same as the angle of reflection.

The angle between the normal and the incident ray is known as the angle of incidence.

Similarly, the angle between the reflected ray and normal is known as the angle of reflection.

From the above-mentioned information, we can conclude,

<i = <r

where,

<i is the angle of incidence and

<r is the angle of reflection,

From the question, we know that,

<i + <r = 120°

Also, from the above equation, we can conclude

2<i = 120°

<i = 60°

Hence, the angle of incidence is 60°