A parallel beam of light is incident on a sys | vedclass

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(A) For a parallel beam of light to emerge parallel after passing through a system of two convex lenses,the intermediate image formed by the first len

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$30$

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(A) For a parallel beam of light to emerge parallel after passing through a system of two convex lenses,the intermediate image formed by the first lens must act as an object at the focal point of the second lens.The first lens with focal length $f_1 = 20\, cm$ converges the incoming parallel rays at its focal point,which is at a distance of $20\, cm$ from the first lens.For the second lens with focal length $f_2 = 10\, cm$ to render these rays parallel again,the rays must appear to come from its focal point. Thus,the focal point of the first lens must coincide with the focal point of the second lens.The distance $d$ between the two lenses is given by the sum of their focal lengths:$d = f_1 + f_2$$d = 20\, cm + 10\, cm = 30\, cm$.Therefore,the distance between the two lenses should be $30\, cm$.

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