Post-UTME Physics 2016 Objective — Question 8

Question 8 of 20 from the Post-UTME Screening (Post-UTME) Physics 2016 Objective paper, with the correct answer and a full explanation.

Calculate the focal length of a converging lens which forms a real image of magnification 4 when the object distance is 15cm.

Explanation

For a real image, v = m x u = 4 x 15 = 60cm. Using 1/f = 1/v + 1/u = 1/60 + 1/15 = 1/60 + 4/60 = 5/60 = 1/12, so f = 12cm.

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