Question

If a plane mirror reflecting a ray of incident light is rotated in the plane of incidence through an angle $\theta$, then

• A. Reflected ray does not rotate
• B. Reflected ray rotate through an angle $\theta$
• C. Reflected ray rotate through an angle $2\theta$
• D. Incident ray is fixed

Answer 1

The correct option is C Reflected ray rotate through an angle $2\theta$

Consider a plane-mirror and a fixed incident ray of light reflecting from the surface at an angle . Before the mirror has rotated, the angle of incidence is is the angle of reflection. If the mirror is rotated through an angle the normal is rotated by an angle and thus the angle of incidence increases to +. Therefore, the angle of reflection must also increase by tow The difference between the final angle of reflection and the initial angle of reflection and is $2\theta .$