Practice MCAT Question - Q11 - Answer!
What is the focal length of a lens that forms a virtual image 30 cm from the lens when a real object is placed 15 cm from the lens?
A. 10 cm
B. 15 cm
C. 30 cm
D. 45 cm
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The correct answer is (C). The distance is given by the thin lens equation,
1/f = 1/p + 1/q. Since the image formed is virtual, the sign of q is negative.
Therefore:
1/f = 1/p - 1/q = 1/15 - 1/30 = 1/30
f = 30 cm
