In Young’s experiment, two coherent sources are placed 0.90 mm apart and fringes are observed 1 m away. If the second dark fringe is at distance 1 mm from central bright fringe, wavelength of monochromatic light used is:
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Question

In Young’s experiment, two coherent sources are placed 0.90 mm apart and fringes are observed 1 m away. If the second dark fringe is at distance 1 mm from central bright fringe, wavelength of monochromatic light used is:

Options

G1 Physics · Accepted Answer

Step 1: n-th dark fringe yₙ = (2n − 1)λD/(2d). Step 2: For n = 2: y = 3λD/(2d). Solve λ = 2yd/(3D). Step 3: λ = 2(1 × 10⁻³)(0.9 × 10⁻³)/(3 × 1) = 0.6 × 10⁻⁶ m = 6 × 10⁻⁵ cm. Final answer: (D) 6 × 10⁻⁵ cm.