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Question #43583

Difficulty: 8/10 | 🟢 Free

The Question

In a Young's Double Slit Experiment (YDSE), two identical slits emit coherent light of intensity I0I_0 and optical angular frequency ωopt\omega_{opt}. An electro-optic modulator is placed in front of one of the slits, introducing a time-varying phase shift ϕ(t)=αV(t)\phi(t) = \alpha V(t), where α\alpha is a positive constant in rad/V\text{rad/V} and V(t)V(t) is the applied voltage. The voltage is supplied by an ideal L−CL-C circuit (inductor LL, capacitor CC). At t=0t=0, the capacitor is fully charged to a voltage V0V_0 and the current is zero. Assume the L−CL-C oscillation frequency is much smaller than ωopt\omega_{opt}. Given the integral identity 12π∫02πcos⁡(xcos⁡θ)dθ=J0(x)\frac{1}{2\pi} \int_0^{2\pi} \cos(x \cos \theta) d\theta = J_0(x), where J0(x)J_0(x) is the zeroth-order Bessel function of the first kind, what is the time-averaged intensity ⟨I⟩\langle I \rangle at the central point on the screen (where the geometrical path difference is zero) over one complete period of the L−CL-C oscillation?

Options

  • A.

    2I0[1+J0(αV0)]2I_0 [1 + J_0(\alpha V_0)]

  • B.

    4I0cos⁡2(αV02)4I_0 \cos^2\left(\frac{\alpha V_0}{2}\right)

  • C.

    4I04I_0

  • D.

    2I0[1+J0(αV02)]2I_0 \left[1 + J_0\left(\frac{\alpha V_0}{\sqrt{2}}\right)\right]

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Intensity Distribution in YDSE|L-C Circuit Analogy

Why This Question Is Tricky

Common Mistakes

This question tests the transition from static interference models to dynamic, time-averaged intensity distributions.

Students commonly fall into the trap of averaging the phase shift first (⟨ϕ⟩=0\langle \phi \rangle = 0) and substituting it into the static formula to get 4I04I_0, or they incorrectly use the RMS or maximum voltage directly in the static equation.

The lethal collision occurs when they fail to recognize that the interference term cos⁡(ϕ(t))\cos(\phi(t)) is a non-linear function of the oscillating charge.

Correct physical analysis requires applying the time-average integral directly to the instantaneous intensity function, which maps the sinusoidal LC circuit discharge to a Bessel function dependency for the optical intensity.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterWave Optics - Class 12
ConceptIntensity Distribution in YDSE
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree