Question

A parallel beam of light of wavelength 600 nm is incident normally on a slit of width d. If the distance between the slits and the screen is 0.8 m and the distance of 2nd order maximum from the center of the screen is 15 mm. The width of the slit is

• A. 40 $\mu m$
• B. 80 $\mu m$
• C. 160 $\mu m$
• D. 200 $\mu m$

Answer 1

The correct option is B 80 $\mu m$

Distance of $2^{nd}$ order maximum form the centre of the screen

$x=\frac{5}{2}\frac{D\lambda }{d}$

Here, $D=0.8m,x=15mm=15\times {10}^{-3}m$

$\lambda =600nm=600nm=600\times {10}^{-9}m$

$\therefore d=\frac{5}{2}\cdot \frac{D\lambda }{x}=\frac{5}{2}\times \frac{0.8\times 600\times {10}^{-9}}{15\times {10}^{-3}}=80\mu m$