MHT CET · Physics · Wave Optics

In Young's double slit experiment, the intensity of light at a point on the screen where the path difference is \(\lambda\) is \(x\) units, \(\lambda\). being the wavelength of light used. The intensity at a point where the path difference is \(\frac{\lambda}{4}\) will be \(\left(\cos 2 \pi=1, \cos \frac{\pi}{2}=0\right)\)

A \(\frac{\mathrm{x}}{4}\)
B \(\frac{x}{2}\)
C x
D zero

Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{x}{2}\)

Step-by-step Solution

Detailed explanation

When path difference \(=\lambda\)
Phase difference
\(\begin{aligned}
& \quad \Delta \phi=\frac{2 \pi}{\lambda} \times \lambda=2 \pi \\
& \\
& I=4 I_0 \cos ^2\left(\frac{\phi}{2}\right) \\
& \\
& x=4 I_0 \cos ^2\left(\frac{2 \pi}{2}\right)=4 I_0 \\
& \therefore \quad \\
& x=4 I_0
\end{aligned}\)
When path difference \(=\frac{\lambda}{4}\)
Phase difference
\(\begin{aligned}
& \Delta \delta=\frac{2 \pi}{\lambda} \times \frac{\lambda}{4}=\frac{\pi}{2} \\
& I=4 I_0 \cos ^2\left(\frac{\frac{\pi}{2}}{2}\right)=2 I_0
\end{aligned}\)
Intensity, \(x^{\prime}=\frac{x}{2}\)

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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