A thin convex lens of focal length 20 cm has a plane rear surface silvered. Neglect separation. Light traverses the lens twice. Find the effective focal length.
Options

Question

A thin convex lens of focal length 20 cm has a plane rear surface silvered. Neglect separation. Light traverses the lens twice. Find the effective focal length.

G1 Physics · Accepted Answer

Lens power acts twice; plane mirror adds zero power. F=f/2=10.00 cm.