Two coherent sources P and Q produce interference at point A on the screen where there is a dark band which is formed between 4th bright band and 5th bright band. Wavelength of light used is 6000 Å. The path difference between PA and QA is

Options

A. `104xx10^-4cm`
B. `2.7xx10^-3cm`
C. `405xx10^-4cm`
D. `6.2xx10^-4cm`

Answer

B

Explanation

Path difference `Deltax` is given by `(lambdadelta)/(2pi)`
[Where, `lambda` =wavelength of light, `delta` =phase difference]
For n=4th dark fringe
`delta=(2n-1)pi`
`delta=(8+1)pi=9pi`
`Deltax=(lambda9pi)/(2pi)=9/2lambda=9/2xx6xx10^-7`
=`2.7xx10^-6m=2.7xx10^-04cm`