Q. A beam of light of wavelength 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between the 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
Explanation
(d) $\beta = \frac{\lambda D}{d} = \frac{600 \times 10^{- 9} \times 2}{1 \times 10^{- 3}} = 12 \times 10^{- 4}\ m$
So, distance between the first dark fringes on either side of the central bright fringe
$X = 2\beta$
$= 2 \times 12 \times 10^{- 4}\ m$
$= 24 \times 10^{- 4}\ m = 2.4\ mm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.