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An equiconvex glass lens (n = 1.5) has both radii 20 cm and lies in air. Its focal length is
A40 cm
B30 cm
C20 cm
D10 cm
Answer & Solution
Correct answer: C. 20 cm
1/f = (1.5 - 1)(1/20 + 1/20) = 1/20, so f = 20 cm.
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