Question

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

Answer 1

Correct Answer - B
In between `4^(th)` bright and `5^(th)` bright there is `5^(th)` dark band.
`:.` path diff. `=(2n-1)(lamda)/(2)`
`=(2xx5-1)(lamda)/(2)=4.5lamda`
`=4.5xx6xx10^(-7)`
`=27.0xx10^(-7)m=27xx10^(-5)cm`
`=2.7xx10^(-4)cm`