Question

# A beam of light constituting of two wavelengths 6000∘A and 5200∘A is used to obtain interference fringes in a Young's double slit experiment. The distance between the slits is 2 mm and the distance between the plane of the slits and the screen is 120 cm. The least distance from the central maximum where the bright fringes due to both the wavelengths coincide is

A
3.056 cm
B
2.156 cm
C
0.156 cm
D
3.156 cm

Solution

## The correct option is B 0.156 cmβ1=λ1Dd;β2=λ2Dd β1β2=λ1λ2=65005200=54 or, 4β1=5β2 ⇒ Distance of 4th bright fringe due to λ1 = Distance of 5th bright fringe due to λ2 or, x=4β1=5β2 or, x=4λ1Dd=0.156 cm.

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