Name the spherical mirror which has:

(a) Virtual principal focus.

(b) Real principal focus.

A ray of light strikes a plane mirror PQ at an angle of incidence of 30°, is reflected from the plane mirror and then strikes a second plane mirror QR placed at right angles to the first mirror. The angle of reflection at the second mirror is:

A) 30°

B) 45°

C) 60°

D) 90°

Explain how to read the following message which was found on some blotting paper:

Out of convex mirror and concave mirror, whose focus is situated behind the mirror?

Find the focal length of a concave mirror whose radius of curvature is 30 cm.