Question

A beam of light of $\lambda =600nm$ from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2m away. The distance between first dark fringes on either side of the central bright fringe is

• A. 1.2 cm
• B. 1.2 mm
• C. 2.4 cm
• D. 2.4 mm

Answer 1

Answer: (D)

2.4 mm

Angular width of $1^{st}$ maxima
$2\theta =\frac{2\lambda }{a}$
Linear width of $1^{st}$ maxima $=\left(D\right)\left(2\theta \right)=\frac{2\lambda D}{a}=\frac{2\times (600\times {10}^{-9})\left(2\right)}{1\times {10}^{-3}}=2.4mm$