A convex lens A of focal length 20cm and a concave lens B of focal length 5cm are kept along the same axis with the distance d between them- If a prallel beam of light falling on A leaves B as a parallel beam- then the distance d in cm will be15253050

Question

Toppr Admin · Accepted Answer

The correct option is A 15d-f1-x2212-f2By using the formula1f1-1f1-x2212-df1f2-1FFor the emergent beam to parallelP-0-F-x3B1-x21D2-120-x2212-15-d100-0-x21D2- d-15

A convex lens $A$ of focal length $20 c m$ and a concave lens $B$ of focal length $5 c m$ are kept along the same axis with the distance $d$ between them. If a prallel beam of light falling on $A$ leaves $B$ as a parallel beam, then the distance $d$ in cm will be
$15$
$25$
$30$
$50$

The correct option is A $15$
$d = f_{1} - f_{2}$
By using the formula
$\frac{1}{f_{1}} + \frac{1}{f_{1}} - \frac{d}{f_{1} f_{2}} = \frac{1}{F}$
For the emergent beam to parallel
$P = 0, F = α$
$\Rightarrow \frac{1}{20} - \frac{1}{5} + \frac{d}{100} = 0$
$\Rightarrow$ $d = 15$

A convex lens A of focal length 20cm and a concave lens B of focal length 5cm are kept along the same axis with the distance d between them. If a prallel beam of light falling on A leaves B as a parallel beam, then the distance d in cm will be15253050

The correct option is A 15d=f1−f2By using the formula1f1+1f1−df1f2=1FFor the emergent beam to parallelP=0,F=α⇒120−15+d100=0⇒ d=15

A convex lens $A$ of focal length $20 c m$ and a concave lens $B$ of focal length $5 c m$ are kept along the same axis with the distance $d$ between them. If a prallel beam of light falling on $A$ leaves $B$ as a parallel beam, then the distance $d$ in cm will be
$15$
$25$
$30$
$50$

The correct option is A $15$
$d = f_{1} - f_{2}$
By using the formula
$\frac{1}{f_{1}} + \frac{1}{f_{1}} - \frac{d}{f_{1} f_{2}} = \frac{1}{F}$
For the emergent beam to parallel
$P = 0, F = α$
$\Rightarrow \frac{1}{20} - \frac{1}{5} + \frac{d}{100} = 0$
$\Rightarrow$ $d = 15$