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. 0.75
B. 1.5
C. 3
D. 4.5

Answer

B

Explanation

For dark fringe
`S_(1)P-S_(2)P= ((2n-1)lambda)/(2)`
n= 3 and `lambda= 6000 A`
`S_(1)P-S_(2)P= ((2 xx 3-1) xx 6000 xx 10^(-10))/(2)= 1.5 xx 10^(-6) m = 1.5` micron