1.

A converging glass lens with a refractive index of 1.5 has a focal length of f in air. When it is completely immersed in a liquid of refractive index 2, its focal length and nature will be respectively (a) 2f and converging (b) 3f and converging (c) 2f and diverging (d) 3f and diverging

Answer»

Correct Answer is: (c) 2f and diverging

Let k = 1/R1 - 1/R2 .

∴ 1/f = (1.5 - 1)k

and 1/f' = (1.5/2 - 1) k = (- 0.5/2) 2/f = - 0.5/f.

∴ f' = -2f.



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