CBSE Class 12 Physics 2022 Term 2 Outside Delhi Set 3 Solved Paper

Question : 3

Total: 5

A beam of light consisting of two wavelengths 600‌nm and 500‌nm is used in Young's double slit experiment. The silt separation is 1.0‌mm and the screen is kept 0.60m away from the plane of the slits. Calculate:
(i) the distance of the second bright fringe from the central maximum for wavelength 500‌nm, and
(ii) the least distance from the central maximum where the bright fringes due to both the wavelengths coincide.
3

Solution:

(i) Distance of 2nd bright fringe from central maximum =

2λD

2×500×10−9×0.6

1×10−3

=6×10−4m
(ii)

nλ1D

(n+1)λ2D

Or, nλ1=(n+1)λ2
Or,

(n+1)

λ2

λ1

Or,

(n+1)

500

600

∴n=5
So, least distance from central maximum
=

5×600×10−9×0.6

1×10−3

=18×10−4m

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