Two coherent sources $S_1, S_2$ and a screen are arranged as shown in the figure. If the distance between the two coherent sources is $n \lambda$ and the distance of the screen from the nearer coherent source is D, then the distance of the first bright fringe on the screen from the point ' $\mathrm{O}$ ' is ( $\lambda$ is the wavelength of the light emitted by the coherent sources )

• A

  $\sqrt{\frac{D(D+n \lambda)}{n}}$
• Correct answer
  B

  $\sqrt{\frac{2 D(D+n \lambda)}{n}}$
• C

  $\sqrt{\frac{3 \mathrm{D}(\mathrm{D}+\mathrm{n} \lambda)}{\mathrm{n}}}$
• D

  $\sqrt{\frac{D(D+n \lambda)}{2 n}}$

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