SF P1 6

JEE Advanced Sample Questions › Optics questions › SF P1 6

There is an euiconvex glass lens with radius of each face as R and aÎ¼g = 3/2 and aÎ¼w = 4/3 . If there is water in object space and air in image space, then the focal length is:

A) 2R B) R

C) 3 R/2 D) R²

#Physics #Optics

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2 Answers

Lokesh Verma ·Feb 20 '10 at 10:50

$\\\frac{\mu_g}{v}-\frac{\mu_w}{u}=\frac{\mu_g-\mu_w}{R}\\\frac{\mu_g}{v}-\frac{\mu_w}{-\infty}=\frac{\mu_g-\mu_w}{R} \\\frac{\mu_gR}{\mu_g-\mu_w}=v$

$\\\frac{\mu_a}{v}-\frac{\mu_g}{u}=\frac{\mu_a-\mu_g}{-R}\\\frac{\mu_a}{f}-\frac{\mu_g(\mu_g-\mu_w)}{\mu_gR}=\frac{\mu_a-\mu_g}{-R} \\\frac{\mu_a}{f}=\frac{2\mu_g-\mu_w-\mu_a}{R} \\f=\frac{3R}{2}$