If the focal length of a camera is 20cm; the distance from the film at which the lens must be set to produce a sharp image of 100cm away is?

A. 17cm
B. 20cm
C. 25cm
D. 100cm

Correct Answer:

Option A = 17cm

Explanation

F = 20cm

V = 100cm

U = ?

1/U + 1/V = 1/F
1/20 + 1/100 = 1/F
5 + 1/100 = 1/F
F = 100/6

= 16.7cm

= 17cm