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Question #42024

Difficulty: 8/10 | 🟢 Free

The Question

A primary coil is driven by an alternating current I1(t)=I0sin⁡(ωt)I_1(t) = I_0 \sin(\omega t). A secondary coil with self-inductance LL and negligible resistance is magnetically coupled to the primary with a mutual inductance M>0M > 0. The secondary coil is connected in series with a load ZZ. The reference direction for the secondary current I2(t)I_2(t) is chosen such that positive I1I_1 and positive I2I_2 produce magnetic flux in the same direction in the core. Let Δϕ\Delta \phi be the phase difference such that the steady-state secondary current is I2(t)=I20sin⁡(ωt+Δϕ)I_2(t) = I_{20} \sin(\omega t + \Delta \phi) with I20>0I_{20} > 0. If ΔϕL\Delta \phi_L is the phase difference when ZZ is an ideal inductor L0L_0, and ΔϕC\Delta \phi_C is the phase difference when ZZ is an ideal capacitor C0C_0 (where 1ωC0>ωL\frac{1}{\omega C_0} > \omega L), what are the values of ΔϕL\Delta \phi_L and ΔϕC\Delta \phi_C respectively?

Options

  • A.

    π\pi and 00

  • B.

    −π2-\frac{\pi}{2} and π2\frac{\pi}{2}

  • C.

    00 and π\pi

  • D.

    π2\frac{\pi}{2} and −π2-\frac{\pi}{2}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Multi-Concept_Bridge

Master problems that require linking physics and math concepts to solve complex competitive questions.

Concepts Behind This Question

The Directional Sign Convention|Lenz’s Law Energy Conservation|Transformer Flux Linkage

Why This Question Is Tricky

Common Mistakes

This question tests the rigorous application of Lenz's Law and directional sign conventions in coupled circuits.

Students commonly rely on rote memorization, assuming an inductor causes a −π/2-\pi/2 phase lag and a capacitor causes a +π/2+\pi/2 phase lead relative to the source.

However, by explicitly defining the reference direction for the secondary current such that the fluxes add, the induced EMF carries a strict negative sign (E=−dΦ/dt\mathcal{E} = -d\Phi/dt).

This forces the secondary current to be exactly out of phase (π\pi) for an inductive load to oppose the primary flux change, and exactly in phase (00) for a dominant capacitive load due to the double time-derivative flipping the sign.

Failing to account for the coordinate-dependent flux linkage leads to standard phase-errors.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterMotion in a Straight Line - Class 11 Part 1
ConceptThe Directional Sign Convention
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree