All Free Electrical Engineering MCQs with Answers

• A. change the direction of magnetic lines
• B. amplify flux
• C. restore lost flux
• D. provide a closed path for flux

Explanation: A keeper is a piece of soft iron placed across the poles of a permanent magnet to complete the magnetic circuit.

• A. the field of a set of parallel conductors
• B. the field of a single conductor
• C. the field in which all lines of magnetic flux are parallel and equidistant
• D. none of the above

Explanation: A uniform magnetic field has the same magnitude and direction throughout the region.

• A. reluctance of conductor
• B. resistance of conductor
• C. A. and B. both in the same way
• D. none of the above

Explanation: Both resistance, R = ρl/A, and magnetic reluctance, S = l/(μA), vary inversely with cross-sectional area.

• A. the voltage across the two ends of exciting coil
• B. the flow of an electric current
• C. the sum of all currents embraced by one line of magnetic field
• D. the passage of magnetic field through an exciting coil

Explanation: By Ampere's circuital law, magnetomotive force around a magnetic path equals the algebraic sum of currents enclosed by that path…

• A. Decreases
• B. Increases
• C. Remains same
• D. First increases and then decreases depending on the depth of iron in¬sertion

Explanation: Introducing an iron core greatly increases the permeability inside the coil.

• A. 2 AT
• B. 4 AT
• C. 6 AT
• D. 10 AT

Explanation: Magnetic potential difference, or mmf drop, is H multiplied by the gap length: 200 AT/m × 0.02 m = 4 AT. Hence option b is obtained.

• A. the highest permeability of the iron rod
• B. the lowest permeability of the iron rod
• C. the permeability at the end of the iron rod
• D. the permeability almost in non-magnetised state

Explanation: Initial permeability is the permeability measured from the nearly unmagnetised state, at the beginning of the magnetisation curve.

• A. decreases with increasing cross sectional area of material
• B. increases with increasing cross-sec-tional area of material
• C. does not vary with increasing cross-sectional area of material
• D. any of the above

Explanation: Magnetic reluctance is given by ℜ = l/(μA), so increasing the cross-sectional area provides an easier path for flux and decreases…

• A. the dipole moment
• B. monopole moment
• C. A. and B. both
• D. none of the above

Explanation: A bar magnet has two opposite poles separated by a distance, so it behaves as a magnetic dipole and possesses a dipole moment.

• A. It assures a position right angle to magnetic field
• B. It starts rotating
• C. It assures a position which follows a line of magnetic flux
• D. None of the above

Explanation: A compass needle is itself a small magnet, so its north pole aligns with the local magnetic field direction.

• A. Ferromagnetic
• B. Paramagnetic
• C. Diamagnetic
• D. None of the above

Explanation: Diamagnetic materials have very weak, opposing magnetisation and are therefore less important in common engineering magnetic applications.

• A. a line vertical to the flux lines
• B. the mean length of a ring shaped coil
• C. a line of magnetic flux in a non-uniform field
• D. a line of magnetic flux which does not follow the designed path

Explanation: Stray flux is the portion of magnetic flux that leaves the intended magnetic circuit and travels through surrounding air or other…

• A. Silver
• B. Copper
• C. Silver and copper
• D. Iron

Explanation: Silver and copper are diamagnetic, meaning they are weakly repelled by a magnetic field.

• A. Yes
• B. No

Explanation: Self-inductance is the induced emf per unit rate of change of current, expressed as e = L(di/dt), so the rate must be in amperes per…

• A. Resistance only
• B. Inductance only
• C. Capacitance only
• D. Inductance and capacitance

Explanation: Inductance opposes a change in current by producing a back emf, e = -L(di/dt).

• A. variation in coil current
• B. variation in voltage to the coil
• C. change of number of turns of coil
• D. the resistance of magnetic path

Explanation: The self-induced emf is governed by e = L(di/dt), with inductance depending on turns and magnetic-path reluctance; applied voltage is not…

• A. unchanged inductance
• B. increased inductance
• C. zero inductance
• D. reduced inductance

Explanation: A crack introduces an air gap in the magnetic path, increasing reluctance.

• A. self-inductance of two coils only
• B. mutual inductance between two coils only
• C. mutual inductance and self inductance of two coils
• D. none of the above

Explanation: The coefficient of coupling is k = M/√(L₁L₂), so it depends on mutual inductance and the self-inductances of both coils.

• A. 5 mH
• B. 10 mH
• C. 5 H
• D. 10 H

Explanation: Using V = L(di/dt), the current changes by 12 − 8 = 4 A in 1 second, so L = 20/4 = 5 H. Therefore, option c is correct.

• A. 3500 mH
• B. 350 mH
• C. 250 mH
• D. 150 mH

Explanation: From V = L(di/dt), L = 0.350/1 = 0.350 H, which equals 350 mH. The voltage must be converted from millivolts before calculating.