Question

The distances of interference point on a screen from two slits are $18\mu m$ and 12.3 $\mu$ m. If the wavelength of light used is $6\times {10}^{-7}m$ then the number of dark or bright fringe formed there will be -

• A. $8^{th}$dark
• B. $9^{th}$ bright
• C. ${10}^{th}$ dark
• D. ${11}^{th}$ dark

Answer 1

Answer: (B)

$9^{th}$ bright

$\begin{array}{c}\Delta =d\sin \theta \\ 5.7\mu m=d\theta \\ \theta =\frac{5.7\mu n}{d}\\ x=\frac{\Delta D}{d}\\ \frac{\Delta }{x}=\frac{5.7}{6\times {10}^{-7}}\\ \frac{\Delta }{x}=\frac{56}{6}=\frac{19}{2}\\ Hence,wehave\\ \frac{\Delta }{x}=9\frac{1}{2}\end{array}$