A convex lens $A$ of focal length 20 cm and a concave lens $B$ of focal length 56 cm are kept along the same axis with the distance $d$ between them. If a parallel beam of light falling on $A$ leaves $B$ as a parallel beam, then distances $d$ in cm will be

Question

Dr. Abubacker · Accepted Answer

(b) $P = \frac{1}{f_{1}} + \frac{1}{f_{2}} - \frac{d}{f_{1}f_{2}} = 0$
$	herefore\frac{1}{f_{1}} + \frac{1}{f_{2}} = \frac{d}{f_{1}f_{2}}$
$\frac{1}{20} - \frac{1}{56} = \frac{d}{20( - 56)}$
$\frac{56 - 20}{20 	imes 56} = \frac{d}{- 20 	imes 56}$
$d = - 36\ cm$

Q. A convex lens $A$ of focal length 20 cm and a concave lens $B$ of focal length 56 cm are kept along the same axis with the distance $d$ between them. If a parallel beam of light falling on $A$ leaves $B$ as a parallel beam, then distances $d$ in cm will be

Explanation

Reviewed by Dr. Abubacker

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