Question

A convex lens having power 5 D is placed in contact with a concave lens having power-3 D. The focal length of the combination will be?

• A. -50 cm
• B. -0.5 cm
• C. 50 cm
• D. 0.5 cm

Answer 1

Answer:

C. 50 cm

• The power of the combination is given by P = P1 + P2 = 5D + (-3D) = 2D.

• The focal length is given by f = 1/P= 1/2D = 0.5m = 50cm