Question

In a biconvex lens \(R_1 ,R_2\) and f are 15 cm, 10 cm and 12 cm respectively find refractive index of lens.

(1) 2

(2) \(\frac{3}{4}\)

(3) \(\frac{4}{3}\)

(4) \(\frac{3}{2}\)

Answer 1

Correct option is : (4) \(\frac{3}{2}\) 

\(\frac{1}{f} = (\mu - 1) \left( \frac{1}{R_1} - \frac{1}{R_2}\right)\)

\(\frac{1}{12} = (\mu - 1) \left(\frac{1}{15}+ \frac{1}{10}\right)\)

\(\frac{1}{12} = (\mu - 1) \frac{1}{5} \left(\frac{5}{6}\right)\)

\(\frac{1}{2} + 1 = \mu\)