When a plane mirror is rotated by 12° clockwise about the point where a ray of light hits it, the incident ray stays fixed. By how many degrees does the ref...
Question 1 Report
When a plane mirror is rotated by 12° clockwise about the point where a ray of light hits it, the incident ray stays fixed.
By how many degrees does the reflected ray rotate?
Answer Details
When a plane mirror is rotated by an angle \( \theta \) while the incident ray remains fixed, the reflected ray rotates by \( 2\theta \). This is a standard result from the law of reflection.
The reasoning is as follows: rotating the mirror by \( \theta \) also rotates the normal by \( \theta \). The angle of incidence (measured from the normal) therefore changes by \( \theta \), and since the angle of reflection must equal the angle of incidence, the angle of reflection also changes by \( \theta \). The total angular shift of the reflected ray is the sum of both changes, which is \( 2\theta \).
With a mirror rotation of 12°, the reflected ray rotates by \( 2 \times 12° = 24° \). This \( 2\theta \) relationship is widely used in instruments such as the mirror galvanometer, where a small mirror rotation produces a doubled deflection of the reflected light beam.
Download The App On Google Playstore
Everything you need to excel in your exams
