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(B) For a parallel beam of light to emerge from a system of two convex lenses,the intermediate image formed by the first lens must coincide with the f

Vedclass · Accepted Answer

$30$

Vedclass · Answer

(B) For a parallel beam of light to emerge from a system of two convex lenses,the intermediate image formed by the first lens must coincide with the focal point of the second lens.$1$. The first lens $L_1$ with focal length $f_1 = 20 \, cm$ receives parallel rays,so it forms an image at its focal point,at a distance of $20 \, cm$ from $L_1$.$2$. This image acts as an object for the second lens $L_2$ with focal length $f_2 = 10 \, cm$. For the rays to emerge parallel from $L_2$,this object must be placed at the focal point of $L_2$.$3$. Therefore,the distance between the two lenses $d$ must be the sum of their focal lengths:$d = f_1 + f_2 = 20 \, cm + 10 \, cm = 30 \, cm$.Thus,the correct distance is $30 \, cm$.

$A$ parallel beam of light is incident on a system of two convex lenses with focal lengths $f_1 = 20 \, cm$ and $f_2 = 10 \, cm$. What should be the distance between the two lenses so that the rays,after refraction from both lenses,emerge as a parallel beam? (in $cm$)

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