Angular width of central maximum in Fraunhofer diffraction for wavelength λ = 6000 Å is θ₀. When same slit is illuminated by another monochromatic light, angular width is reduced by 30%. The wavelength of this light is:
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Question

Angular width of central maximum in Fraunhofer diffraction for wavelength λ = 6000 Å is θ₀. When same slit is illuminated by another monochromatic light, angular width is reduced by 30%. The wavelength of this light is:

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G1 Physics · Accepted Answer

Step 1: For a fixed slit width a, angular width of central maximum θ = 2λ/a. Step 2: New angular width is 70% of the previous value, so λ₂ = 0.70 λ₁. Step 3: λ₂ = 0.70 × 6000 Å = 4200 Å. Final answer: (B) 4200 Å.