Q: A small plane mirror is rotating at constant frequency of n rotations per second. With what linear velocity (in m/s) will a light spot move along a spherical screen of radius of curvature of R meter if the mirror is at the center of curvature of the screen ?

**Solution :** If a mirror rotates through an angle θ , the image rotates through an angle 2θ . Therefore, the linear speed of the light spot is

v = 2 R ω = 2 R (2 π n) = 4 π n R