A beam of light of wavelength 600 nm from a distant source falls on a single slit of width 1 mm and resulting diffraction pattern is observed on screen 2 m away. The distance between first dark fringes on either side of central bright fringe is:
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Question

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

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G1 Physics · Accepted Answer

Step 1: Distance of first minimum from centre y = λD/a. Step 2: λ = 600 × 10⁻⁹ m, D = 2 m, a = 1 × 10⁻³ m. Step 3: y = (600 × 10⁻⁹ × 2)/(10⁻³) = 1.2 × 10⁻³ m = 1.2 mm. Step 4: Distance between two first dark fringes = 2y = 2.4 mm. Final answer: (D) 2.4 mm.