Question

the power of concave lens is -4.5 D and is made of a material of refractive index 1.6. catculate the radii of curvature of the lens?​

Answer 1

Answer:

The radii of curvature of the lens is 26.7cm .

Explanation:

Using lens makers formula, assuming the lens is thin  and it is used in air.

Lens maker's formula:

$P = \frac{1}{f} = (\mu - 1)(\frac{1}{R_1}-\frac{1}{R_2} )$

For Concave lens,Lens maker's formula is

     $P = \frac{1}{f} = (\mu - 1)(\frac{1}{(-R_1)}-\frac{1}{R_2} )$  [For concave lens, $R_1$ is negative]

 → $P = \frac{1}{f} = -(\mu - 1)(\frac{1}{R_1}+\frac{1}{R_2} )$   ..............................(i)

Now,$R_1 = R_2$  , $\mu = 1.6$  and P = -4.5 D

From equation (i),we can write

           $-4.5 = -(1.6 - 1)(\frac{2}{R})$

         → $4.5= \frac{(0.6 \times2)}{R}$

         → $R = \frac{1.2}{4.5} = 0.267 m$ = 26.7 cm

∴ The radii of curvature of the lens is 26.7cm .