Question

On rotating a mirror through an angle of 20°, the reflected ray is found to get deviated through an angle
Ans : 40°. I want explanation. see it is a 65 point question

Answer 1

On rotating a mirror through an angle of 20 degree respectively is found to get debited to an angle 40 degree because the surface of the mirror proving the incident ray is Park maybe not a plane surface it will be rough surface so the reflective ray is 40 Degrees

Answer 2

When a mirror is tilted by “x” degrees, the deviation of the reflected ray becomes “2x” degrees.

Explanation.
Suppose a ray incidents on a plane mirror with an angle “a”degrees, then
Angle of Incidence = a degrees = Angle of Reflection
=> Angle between Incident and Reflected Ray =i+r = 2a
Now, suppose the mirror is tilted through b degrees, such that the normal moves away from the incident ray, then the incident angle will become a+b degrees, then,
Angle of Incidence after tilt = a+b degrees = Angle of Reflection after Tilt
=> Angle between Incident and Reflected Ray after Tilt=i+r = 2a + 2b
Total deviation is equal to the difference between the angles between the rays, which is equal to 2b degrees.
Hence proved.