In a Fresnel biprism experiment, the two positions of lens give separation between the slits as 16cm and 9cm respectively. What is the actual distance of separation?

Options

A. 12.5 cm
B. 12 cm
C. 13 cm
D. 14 cm

Answer

B

Explanation

In biprism, the virtual images act as two coherent sources and from these two virtual images rays superimposed and interference fringes are formed in overlapping region AB on a screen placed at O.

In order to measure the distance 2d between the virtual sources `S_(1)` and `S_(2)`. Glazebrook gave a method, known as magnification method due to Glazebrook. If `d_(1)` and `d_(2)` are distance between real images of `S_(1)` and `S_(2)`, then
`2d=sqrt(d_(1)d_(2))`
Given, `d_(1)=16cm, d_(2)=9cm`
`therefore 2d=sqrt(16xx9)=12 cm`