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Question #43338

Difficulty: 8/10 | 🟢 Free

The Question

A series LCR circuit consists of a capacitor of capacitance C=1 \muFC = 1 \text{ \mu F}, an inductor of effective inductance L=1 HL = 1 \text{ H} with a ferromagnetic core, and an ohmic resistance R=10 \OmegaR = 10 \text{ \Omega}. The circuit is driven by an AC voltage source at its resonant frequency, maintaining a peak steady-state current I0=1 AI_0 = 1 \text{ A}. The ferromagnetic core has a volume V=10−4 m3V = 10^{-4} \text{ m}^3 and the area of its magnetic hysteresis loop (B−HB-H curve) is Ah=100π J/m3A_h = 100\pi \text{ J/m}^3. What is the effective quality factor QQ of this circuit?

Options

  • A.

    25

  • B.

    50

  • C.

    75

  • D.

    100

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Variable_Constraint

Develop pure symbolic logic skills by mastering algebraic constraints without relying on numerical data.

Concepts Behind This Question

Quality Factor (Q-factor)|Hysteresis Loop Area|Average Power over Cycle

Why This Question Is Tricky

Common Mistakes

This question tests the fundamental energy-based definition of the Quality Factor (Q-factor) and the physical reality of core losses in AC circuits.

Students are heavily conditioned to blindly apply the lumped-parameter formula Q=1RLCQ = \frac{1}{R}\sqrt{\frac{L}{C}}, which yields Q=100Q = 100 (Option D).

This formula assumes that all energy dissipation is purely ohmic.

However, in a real inductor with a ferromagnetic core, the hysteresis loop area represents an additional, frequency-dependent energy loss per cycle.

To solve this correctly, the student must abandon the standard formula, calculate the total energy dissipated per cycle (ohmic + hysteresis), and use the foundational definition Q=2π(Estored/Edissipated)Q = 2\pi (E_{\text{stored}} / E_{\text{dissipated}}).

This effectively models the hysteresis as an equivalent series resistance Reff=Rohmic+ω0AhVπI02R_{\text{eff}} = R_{\text{ohmic}} + \frac{\omega_0 A_h V}{\pi I_0^2}.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterAlternating Current - Class 12
ConceptQuality Factor (Q-factor)
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree