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In Young’s double slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths λ 1 = 12000 Å and λ 2 = 10000 Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other ?
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- 6 mm
- 4 mm
- 3 mm
- 8 mm
Correct Option: A
| ∵ y = | d |
&htere4; n1 λ1 = n2λ2
⇒ n1 × 12000 × 10–10 = n2 × 10000 × 10–10
or, n (12000 × 10–10) = (n + 1) (10000 × 10–10)
⇒ n = 5
(∵ λ1 = 12000 × 10–10m; λ2 = 10000 × 10–10 m)
| Hence, ycommon = | d |
| = | 2 × 10–3 |
(∵ d = 2 mm amd D = 2mm)
= 5 × 12 × 10–4 m
= 60 × 10–4 m
= 6 × 10–3 m = 6 mm
