The focal lengths of a convex lens for red, yellow and violet rays are 100 cm, 98 cm and 96 cm respectively. Find the dispersive power of the material of the lens.

Question

Philoid · Accepted Answer

Given that

Focal length of convex lens for red light=f_r = 100cm

Focal length of convex lens for yellow light=f_y = 98cm

Focal length of convex lens for violet light =f_v= 96cm

Let:
μ_r = Refractive index for the red color
μ_y = Refractive index for the yellow color
μ_v = Refractive index for the violet color
Focal length of a lens (f)f is given by

The focal length of a lens is given by

Let, ,

Then,

So, …(i)

…(ii)

…(iii)

From these equations,

Dispersive Power =

=