Question

A plane convex lens is made of refractive index 1.6 . The radius of of convatureof the curved surface is 60 cm the focal length of the lens is ?

Answer 1

Answer:

for plano convex lens

f = R/(μ-1)

f = 60/(1.6-1)

f = 60/0.6

f = 600/6

f= 100cm or 1m

Answer 2

Solution:

Given:

=> Refractive index (μ) = 1.6

$\sf{\implies R_{1}=60\;cm}$

$\implies R_{2}=\infty$

To Find:

=> Focal length of lens

Formula used:

$\sf{\implies \dfrac{1}{f}=(\mu -1)\bigg(\dfrac{1}{R_{1}}-\dfrac{1}{R_{2}}\bigg)}$

Now, put the values in the formula.

$\sf{\implies \dfrac{1}{f}=(\mu -1)\bigg(\dfrac{1}{R_{1}}-\dfrac{1}{R_{2}}\bigg)}$

$\sf{\implies \dfrac{1}{f} =(1.6-1)\bigg(\dfrac{1}{60}-\dfrac{1}{\infty}\bigg)}$

$\sf{\implies \dfrac{1}{f}=(0.6)\bigg(\dfrac{1}{60}\bigg)}$

$\sf{\implies \dfrac{1}{f}=\dfrac{0.6}{60}}$

$\sf{\implies f = \dfrac{60}{0.6}}$

$\large{\boxed{\boxed{\sf{\implies f = 100\;cm}}}}$

Hence, the focal length of the lens is 100 cm.