Question

The focal length of a glass lens for red and violet lights are 100 and 96.8cm respectively. Find the dispersive power of the glass.​

Answer 1

Answer:

According to the problem the focal length of lens red and violet are 100 cm and 96.8 cm respectively.

we know that, if focal length is f

then,

1/f = (μ−1)(1/R1 - 1/R2)

=> (μ−1) = K/f  

where K = 1/(1/R1  −1/R2)  

let fv= focal length for violet, fr = focal length for red.

μv is the coefficient of violer and μr is for red.

μv −1 = K/fv    &    μr −1 = K/fr

μv − μr  = K (1/fv − 1/fr)

Dispersive power = ω = μv − μr = K (1/fv − 1/fr)

Now if we put all the focal length values for violet and red we will get th dispersive power.