In Young's double-slit experiment, the slits are `2mm` apart and are illuminated by photons of two wavelengths `lambda_1=12000Å` and `lambda_2=10000Å`. At what minimum distance from the common central bright fringe on the screen `2m` from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other?

Options

A. 6 mm
B. 4 mm
C. 3 mm
D. 8 mm

Answer

A

Explanation

For last distance,
`n=(lambda_(2))/(lambda_(1)-lambda_(2))`
`=(10000)/(12000-10000)`
`n=5`
`:. X_(5)=(D)/(d)5 lambda`
`=(2xx5xx12xx10^(-7))/(2xx10^(-3))=6xx10^(-3) m`