Radii of curvature of a convex lens are 20 cm and 30 cm and its focal length is 24 cm. Refractive index of the lens will be
Answer & explanation
Correct answer: option 2
$\text{Focal length of lens in air is }\frac{1}{f_a} = (\mu_g - 1)(\frac{1}{R_1} - \frac{1}{R_2})$
$ \frac{1}{24} = (\mu_g - 1)(\frac{1}{20} + \frac{1}{30}) =(\mu_g - 1)\frac{1}{12} $
$ \mu_g - 1 = 0.5$
$\Rightarrow \mu_g = 1.5$