Ray Optics and Optical Instruments - Result Question 32
32. A concave mirror of focal length ’ $f_1$ ’ is placed at a distance of ’ $d$ ’ from a convex lens of focal length ’ $f_2$ ‘. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity.
[2012] The distance ’ $d$ ’ must equal :
(a) $f_1+f_2$
(b) $-f_1+f_2$
(c) $2 f_1+f_2$
(d) $-2 f_1+f_2$
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Answer:
Correct Answer: 32. (c)
Solution:
- (c)
$d=f_2+2 f_1$
