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Two lenses , One concave and the other convex of same power are placed such that their principal axes coincide. If the separation b/w the lenses is x, then ,

a) real image is formed for x=0 only.

(b) real image is formed for all values of x

(c) System will behave like a glass plate for x=0

(d) virtual image is formed for all values of x other than zero.

1 Answer

$\large\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_2}-\frac{x}{f_1f_2}$
$\large\frac{1}{f}=\frac{1}{f_1} -\frac{1}{f_1}+\frac{x}{f_1^2}$
$\large\frac{1}{f}=\frac{x}{f_1^2}$$ => f >0$ for every x
for $x=0,f =\infty$
Hence for $x=0$ system will behave like a glass plate.
Hence c is the correct answer.
answered Feb 19, 2014 by meena.p
 

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