COMEDK · Physics · 26. Wave Optics

In a Fraunhofer diffraction experiment at a single slit using a light of wavelength \(400 \mathrm{~nm}\), the first minimum is formed at an angle of \(30^{\circ}\). The direction \(\theta\) of the first secondary maximum is given by

A \(\sin ^{-1}(2 / 3)\)
B \(\sin ^{-1}(3 / 4)\)
C \(\sin ^{-1}(1 / 4)\)
D \(\tan ^{-1}(2 / 3)\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(\sin ^{-1}(1 / 4)\)

Step-by-step Solution

Detailed explanation

Given, wavelength of used light, \[ \lambda=400 \mathrm{~nm} \] For minima in Fraunhofer diffraction, \(\therefore \quad d \sin 30^{\circ}=1 \times 400\) \(\Rightarrow \quad d=800 \mathrm{~nm}\) For maxima in diffraction, \[ d \sin \theta=(2 n+1) \frac{\lambda}{2} \] For first…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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