Question

A beam of light of wavelength 600 nm from a distant source falls on a single slit I mm wide and the resulting diffraction-pattern is observed on a screen 2m 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. 2.4cm
• D. 2.4mm

Answer 1

Answer: (D)

2.4mm

Answer 2

$\beta =\frac{\lambda D}{d}=\frac{600\times {{10}^{-9}}\times 2}{1\times {{10}^{-3}}}=12\times {{10}^{-4}}\,m$ So, distance between the first dark fringes on either side of the central bright fringe $X=2\beta$ $=2\times 12\times {{10}^{-4}}m$ $=24\times {{10}^{-4}}m$ $=2.4\,mm$