Question

Two monochromatic coherent sources $S_1$ and $S_2$ emitting light of wavelength $\lambda =4000\AA$ are placed along the line normal to the screen as shown in figure. Separation between $S_1$ and $S_2$ is $d=1mm$. If $D=1m,$ then order of bright fringe formed at point O will be

• A. 2000
• B. 2500
• C. 1000
• D. 1500

Answer 1

The correct option is B 2500

Path difference $\Delta x=n\lambda$

$n=\frac{d}{\lambda }=\frac{1}{0.4\times {10}^{-3}}$

$n=2500$