JAMB Physics 1993 Question 27

Question 27

Lenses and Optical Instruments

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

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

Show the answer and explanation

Answer: C (25cm)

Explanation

1/v = 1/f − 1/u = 1/20 − 1/100 = 4/100, so v = 25 cm.