# A convex lens placed between an object and screen forms a sharp image of the object on screen. A glass slab of refractive index n is inserted between object and lens. In order to obtain the sharp image on the screen again the lens has to be displaced by a distance x. What is the thickness of the slab?(adsbygoogle = window.adsbygoogle || []).push({});

I solved it in the following way:

Let t be the thickness of the slab.

Shift in position of image due to the insertion of glass slab = [t(n-1)]n

i.e. x = [t(n-1)]n

t = (nx)/(n – 1)

But the answer given in my book is n/x.

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# Change in position of image due to insertion of glass slab

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