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 $2^{nd}$ order maximum from the centre 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

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