Question

In YDSE, coherent monochromatic light having wavelength 600 nm falls on the slits. First-order bright fringe is at 4.84 mm from central maxima. Determine the wavelength for which the first-order dark fringe will be observed at the same location on screen. `(Take D = 3 m.)`
A. 600 nm
B. 1200 nm
C. 300 nm
D. 900 nm

Answer 1

Correct Answer - b
`(lambda_(1) D)/(d) = 4.84 mm`
Let required wavelength be `lambda_(2)`. Then according to give information,
`(lambda_(2) D)/(2d) = 4.84 mm`
From (i) and (ii),
`(lambda_(1))/((l_(2))/(2)) = 1 implies lambda_(2) = 1200` nm