IGNOU BPHCT 137 2026 - A plane light wave of wavelength falls on a long narrow sli

Question

A plane light wave of wavelength $580\text{ nm}$ falls on a long narrow slit of width $0.5\text{ mm}$ . (i) Calculate the angles of diffraction for the first two minima. (ii) How are these angles influenced if the width of slit is changed to $0.2\text{ mm}$ ? (iii) If a convex lens of focal length $0.15\text{ m}$ is now placed after the slit, calculate the separation between the second minima on either side of the central maximum.

19 Jan 2026

Answer :

Word Count : 318

A plane light wave of wavelength λ = 580 nm = 5.8 × 10⁻⁷ m is incident on a long narrow slit of width a = 0.5 mm = 5 × 10⁻⁴ m. For single-slit diffraction, the condition for minima is a sinθ = mλ, where m = 1, 2, 3, … For the first minimum (m = 1), sinθ₁ = λ / a = (5.8 ×

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