passwella.
Menu

JAMB Physics 1994 Question 35

Question 35

Lenses and Optical Instruments

An object is placed in front of a converging lens of focal length 20cm. The image is virtual and has a magnification of 2. What is the distance of the object from the lens?

  1. A.5cm
  2. B.10cm
  3. C.30cm
  4. D.40cm
Show the answer and explanation

Answer: B (10cm)

Explanation

Virtual image with m = 2: v = −2u. Using 1/u + 1/v = 1/f: 1/u − 1/(2u) = 1/20, so 1/(2u) = 1/20 and u = 10 cm.