Q105 / 150 · MHT CET 2017 · Physics

The distance between two coherent sources is 1 mm. The screen is placed at a distance of 1 m from the sources. If the distance of the third bright fringe is 1.2 mm from the central fringe, the wavelength of light used is

  • Correct answer
    A
    4000 Å
  • B
    5000 Å
  • C
    6000 Å
  • D
    7200 Å

Solution

The position of maxima
yn= nDλd
⇒ λ= yndnD
Here, n=3,  yn=1.2 mm=1.2×10-3 m,
D=1 m,    d=1 mm=1×10-3 m
∴ λ= 1.2 × 10-3 × 1 × 10-33 × 1
=0.4×10-6 m=4× 10-7 m
=4000 Å

Hence, the correct answer is option: 'A'.

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