Two coherent sources A and B of wavelenth `6xx10^(-5)cm` produce interference at ann arbitrary observation point P.
what is the path difference BP-AP if the point P is at a dark band between the third and forth order maxima?

Options

A. `2.1xx10^(-2)cm`
B. `2.1xx10^(-4)cm`
C. `4.2xxx10^(-4)cm`
D. `4.2xx10^(-3)cm`

Answer

B

Explanation

There will be fourth dark band between the third annd fourth maxima (bright band)
for a dark band `BP-AP=(2n-1)(lamda)/(2)`
Here n=4 and `lamda=6xx10^(-5)cm`
`BP-AP=(2xx4-1)xx(6xx10^(-5))/(2)cm=2.1xx10^(-4)cm`