Question

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. $6000\,\mathring{A}$
• B. $5000 \,\mathring{A}$
• C. $3000\,\mathring{A}$
• D. $1500\,\mathring{A}$

Answer 1

Answer: (A)

For second dark fringe $d \sin \theta=2 \lambda$
$\Rightarrow 24 \times 10^{-5} \times 10^{-2} \times \sin 30^{\circ}=2 \lambda$
$\Rightarrow \lambda=6 \times 10^{-7} m =6000 \,\mathring{A}$