Question

A concave mirror of focal length 'f1' is placed at a distance of 'd' from a convex lens of focal length 'f2'. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance 'd' must equal :
(1) 2f1 + f2
(2) –2f1 + f2
(3) f1 + f2
(4) –f1 + f2

Answer 1

1

Answer on Question #42020 - Physics - Acoustics

Question: A concave mirror of focal length 'f1' is placed at a distance of 'd' from a convex lens of focal length 'f2'. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance 'd' must equal: (1) 2f1 + f2 (2) 2f1 + f2 (3) f1 + f2 (4) f1 + f2

Solution. We want the focuses of mirror and lens to coincide, hence, correct answer is (3) f1+f2.

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