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. `1.4xx10^(-4)m`
B. `2.7xx10^(-4)m`
C. `4.5xx10^(-4)cm`
D. `6.2xx10^(-4)cm`

Answer

B

Explanation

There will be 5th dark band between the fourth and fifth bright bands. `therefore n=5`
For the dark band `PA-QA=(2n-1)(lamda)/(2)`
Path difference `=(2xx5-1)(lamda)/(2)=(9lamda)/(2)`
path difference `=(9lamda)/(2)=(9)/(2)xx6000xx10^(-10)m`
`=27xx10^(-7)m`
`=2.7xx10^(-4)cm`