Question

Two lenses , once concave and the other convex of same power are placed such that their principal axes coincide . if the separation between 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 value of x other than zero ​

Answer 1

Hii !!

Solution:-

1/f = 1/f1+1/f2 -x/f1f2

1/f = 1/f1-1/f1+x/f1²

1/f1 = x/f1²

=> f>0 for every x .

for x = 0 , f = infinite

Hence for x = 0 , system will behave like a glass plate .

Since, Ans (b, and c) both option are correct .

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Hope it helps you !!

@Raj❤

Answer 2

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