AP EAMCET · PHYSICS · Wave Optics

In Young's double slit experiment of central fringe is \(I_0\) and fringe width is \(\beta\). If a point is at a distance \(x\) from the central fringe, then the intensity at that point is

A \(I_0 \cos ^2\left(\frac{\pi x}{\beta}\right)\)
B \(I_0 \cos ^2\left(\frac{x}{\beta}\right)\)
C \(\frac{I_0}{4} \cos ^2\left(\frac{\pi x}{\beta}\right)\)
D \(I_0 \cos ^2\left(\frac{\pi \beta}{x}\right)\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(I_0 \cos ^2\left(\frac{\pi x}{\beta}\right)\)

Step-by-step Solution

Detailed explanation

Intensity at distance \(x\) from central maximum is given by \[ I=4 I_0 \cos ^2 \frac{\phi}{2} \] where, \(\phi=\frac{2 \pi d}{\lambda} \sin \theta\) Also, \(\quad \beta=\frac{\lambda D}{d}\) Combining these, we get \[ I=I_0 \cos ^2\left(\frac{\pi x}{\beta}\right) \]

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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