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Question:

A beam of light of λ=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 1.2 cm, 1.2 mm, 2.4 mm, or 2.4 cm?

1.2 cm

2.4 cm

1.2 mm

2.4 mm

Solution:

Angular width of 1st maxima 2θ=2λ/a
Linear width of 1st maxima = (D)(2θ) = 2λD/a
= 2 × (600 × 10⁻⁹)(2) / 1 × 10⁻³
= 2.4mm