An upright image in a convex lens is magnified 3 times. If the focal length of the lens is 30 cm, wh

JAMB Physics 2023 79 views
Source: JAMB · 2023

An upright image in a convex lens is magnified 3 times. If the focal length of the lens is 30 cm, what is the object distance?

  1. 20 cm ✓
  2. 40 cm
  3. 10 cm
  4. 30 cm
Explanation

An upright magnified image from a convex lens is virtual. With magnification 3, the image distance is v = −3u (virtual).

1/f = 1/u + 1/v = 1/u − 1/(3u) = 2/(3u).

So 1/30 = 2/(3u), giving u = 60 ÷ 3 = 20 cm.

Was this explanation helpful?

Something wrong or missing? Tell us — we read every report and fix issues fast.

pastQuestions.ng pastquestions.ng