Magnetism & Magnetic Circuits MCQ [Free PDF] – 13 Objective Questions with Answers

Around a long straight conductor B = μI / (2πr). At the same distance and in the same medium, B is directly proportional to I, so the field gets stronger.

Magnetic flux Φ has an SI unit — the weber (Wb). Flux density B is in tesla (T) = Wb/m².

Mutual inductance satisfies M = k√(L1L2), where 0 ≤ k ≤ 1. The maximum occurs at perfect coupling k = 1: Mmax = √(1×2) mH = √2 mH ≈ 1.414 mH.

C — M = k√(L₁L₂). The coupling coefficient k accounts for the fraction of magnetic coupling between the two coils.

D — L = L₁ + L₂ − 2M. In series opposition the mutually induced flux opposes the self-induced flux in each coil, so 2M is subtracted (series aiding gives +2M).

B — Ferromagnetic material. In ferromagnetic materials (iron, cobalt, nickel) magnetic domains align strongly under an external field, so the material becomes strongly magnetised and can retain it.

Inductance follows L = μN²A/l. Using the intended permeability/geometry data in the question gives approximately 131.94 mH, matching option A.

D — Decreases. For a solenoid L = μN²A/l, so with other factors constant inductance is inversely proportional to length.

A — 5 H. Uncoupled inductors in series carry the same current, so their inductances add directly: 2 + 3 = 5 H.

Yes. Magnetic circuits use direct analogies of Kirchhoff's laws: flux continuity at a junction resembles KCL, and the algebraic sum of MMF drops around a magnetic path equals the applied MMF, analogous to KVL.

For a magnetic circuit of unchanged reluctance, flux is proportional to magnetomotive force: Φ = F/ℜ. Therefore, if flux decreases, the MMF required/producing it also decreases.

Magnetic circuits use an electric-circuit analogy: magnetomotive force drives magnetic flux through reluctance. An air gap greatly increases total reluctance because air has much lower permeability than iron. Key relation: ℜ=l/(μA); Φ=F/ℜ; F=NI.

Exam focus: Air gaps dominate reluctance even when physically short. Common trap: Permeability of magnetic materials is not generally constant with field intensity.

C — Magnetic field. For a straight current-carrying conductor, if the thumb points along the current, the curled fingers give the direction of the magnetic field lines.