Q. A light wave is incident normally over a slit of width $24 \times 10^{- 5}cm$. The angular position of second dark fringe from the central maxima is $30{^\circ}$. What is the wavelength of light
A) $6000\ \mathring{\mathrm{A}}$
B) $5000\ \mathring{\mathrm{A}}$
C) $3000\ \mathring{\mathrm{A}}$
D) $1500\ \mathring{\mathrm{A}}$
Explanation
(a) For second dark fringe $d\sin\theta = 2\lambda$
$\Rightarrow 24 \times 10^{- 5} \times 10^{- 2} \times \sin 30 = 2\lambda$
$\Rightarrow \lambda = 6 \times 10^{- 7}m = 6000\ \mathring{\mathrm{A}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.