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Question #43320

Difficulty: 8/10 | 🟢 Free

The Question

An AC voltage source V(t)=100sin⁡(2000t)V(t) = 100 \sin(2000 t) (where VV is in volts and tt is in seconds) is connected in series with a resistor R=10 ΩR = 10 \ \Omega and a parallel LC tank circuit. The LC tank consists of an ideal inductor L=20 mHL = 20 \text{ mH} and an ideal capacitor C=50 μFC = 50 \ \mu\text{F} connected in parallel. In steady state, the total electromagnetic energy stored in the LC tank fluctuates. Calculate the maximum net work done on the LC tank by the rest of the circuit during any time interval of length Δt=π4000 s\Delta t = \frac{\pi}{4000} \text{ s} (which corresponds to one quarter cycle of the driven AC voltage).

Options

  • A.

    0.12 J0.12 \text{ J}

  • B.

    0.16 J0.16 \text{ J}

  • C.

    0.00 J0.00 \text{ J}

  • D.

    0.20 J0.20 \text{ J}

Check Your Answer

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

LC Circuit Oscillations|Phasor Rotation Convention|Frequency Sensitivity of Z

Why This Question Is Tricky

Common Mistakes

The question tests the student's ability to analyze forced oscillations in an AC circuit, specifically distinguishing between the natural frequency of an LC tank (ω0=1000 rad/s\omega_0 = 1000 \text{ rad/s}) and the driven frequency (ω=2000 rad/s\omega = 2000 \text{ rad/s}).

A common trap is assuming the LC circuit resonates at its natural frequency regardless of the source, leading to the incorrect conclusion that the energy is constant (0.00 J0.00 \text{ J} work done).

Another trap is calculating the maximum energy of the capacitor (0.16 J0.16 \text{ J}) but forgetting that the inductor holds a minimum non-zero energy (0.04 J0.04 \text{ J}) at the exact moment the capacitor is empty, because the driven frequency forces an unequal reactance balance.

This requires applying phasor rotation to find the true steady-state voltage and using the work-energy theorem to equate the work done against conservative forces to the net change in the tank's electromagnetic energy.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectromagnetic Induction - Class 12
ConceptLC Circuit Oscillations
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree