Question

In Young’s double-slit experiment, an interference pattern is obtained on a screen by a light of wavelength 6000 Å, coming from the coherent sources $S_{1}$and $S_{2}$. At certain point P on the screen third dark fringe is formed. Then the path difference $S_{1}P - S_{2}P$ in microns is

• A. 0.75
• B. 1.5
• C. 3.0
• D. 4.5

Answer 1

Answer: (B)

1.5

Answer 2

For dark fringe path difference $\Delta = (2n - 1)\frac{\lambda}{2};$ here n = 3 and λ = 6000 × 10^–10 m

So $\Delta = (2 \times 3 - 1) \times \frac{6 \times 10^{- 7}}{2} = 15 \times 10^{- 7}m = 1.5microns.$