Question

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

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

Answer 1

Answer: (B)

80$\mu m$

Answer 2

Distance of 2^nd order maximum from the centre of the screen

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

Here, $D = 0.8m$

$x = 15mm = 15 \times 10^{- 3}m$

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

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

$= 80 \times 10^{- 6}m = 80\mu m$