Question

Find the nature and order of the interference at O

• A. ${20}^{th}$ minima
• B. ${20}^{th}$ maxima
• C. ${10}^{th}$ maxima
• D. ${10}^{th}$minima

Answer 1

The correct option is B ${20}^{th}$ maxima

The optical path difference ($\Delta x$) between the waves at $P$ is given by
$\Delta x=S_{2}P-S_{1}P=\frac{yd}{D}$
Therefore, $\Delta x=0.01mm$
Also, $\Delta x=n\lambda =0.01mm$
$⟹n=\frac{0.01\times {10}^{-3}}{5000\times {10}^{-10}}=20$
Hence a maxima of ${20}^{th}$ order is obtained at 0.