In Young's double slit experiment, an interference pattern is obtained on a screen by a light of wavelength `6000Å`, coming from the coherent sources `S_1` and `S_2`. At certain point P on the screen third dark fringe is formed. Then the path difference `S_1P-S_2P` in microns is

Options

A. (a) `0.75`
B. (b) `1.5`
C. (c) `3.0`
D. (d) `4.5`

Answer

B

Explanation

For dark fringe at P
`S_1P-S_2P=Delta=(2n-1)lambda//2`
Here `n=3` and `lambda=6000`
So, `Delta=(5lambda)/(2)=5xx(6000)/(2)=15000Å=1.5` micron