All Free Electrical Engineering MCQs with Answers

• A. permeability of the core
• B. the number of their turns
• C. cross-sectional area of their common core
• D. all of the above

Explanation: Mutual inductance depends on core permeability, the turns of both coils, and their shared magnetic cross-sectional area, as reflected by M…

• A. Faraday
• B. Lenz
• C. Newton
• D. Coulomb

Explanation: Lenz’s law states that induced emf and current oppose the change or cause producing them.

• A. self-inductance
• B. mutual inductance
• C. series aiding inductance
• D. capacitance

Explanation: Self-inductance is the property by which a changing current in a coil induces an opposing emf in that same coil.

• A. when more length for the same number of turns is provided
• B. when the number of turns of the coil increase
• C. when more area for each turn is provided
• D. when permeability of the core increases

Explanation: For a coil, L = μN²A/l, so increasing the magnetic-path length l while keeping turns, area and permeability unchanged reduces inductance.

• A. lies perpendicular to the magnetic flux
• B. lies in a magnetic field
• C. cuts magnetic flux
• D. moves parallel to the direction of the magnetic field

Explanation: Faraday's law requires a change in flux linkage, which occurs when a conductor cuts magnetic flux or the flux itself changes.

• A. increase
• B. decrease
• C. remain the same
• D. initially increase and then decrease

Explanation: Inductance is proportional to the core permeability, as shown by L = μN²A/l.

• A. unaffected
• B. doubled
• C. halved
• D. quadrupled

Explanation: Using L = μN²A/l, doubling the turns multiplies inductance by four, while doubling the core length divides it by two.

• A. lesser its weber-turns
• B. lower the e.m.f. induced
• C. greater the flux produced by it
• D. longer the delay in establishing steady current through it

Explanation: In an RL circuit, the current time constant is τ = L/R, so a larger self-inductance makes the current take longer to reach its steady…

• A. Inductance
• B. Condenser
• C. Variable resistor
• D. Resistance

Explanation: An inductor stores energy in its magnetic or electromagnetic field according to W = ½LI².

• A. 50
• B. 20
• C. 0.05
• D. 500

Explanation: For an inductor, the initial current slope is given by di/dt = V/L = 200/10 = 20 A/s.

• A. at 63.2% of its maximum steady value
• B. at the start of the current flow
• C. after one time constant
• D. near the final maximum value of current

Explanation: At the instant a DC voltage is applied, an inductor opposes any sudden change in current, but the current slope is initially maximum…

• A. metre/henry
• B. henry/metre
• C. henry
• D. 1/henry

Explanation: Reluctance is the ratio of magnetomotive force to flux, so its unit is ampere-turn per weber.

• A. reluctivity
• B. permeance
• C. permeability
• D. susceptibility

Explanation: Permeance measures how readily a magnetic circuit carries flux and is defined as the reciprocal of reluctance.

• A. reluctivity
• B. magnetomotive force
• C. permeance
• D. reluctance

Explanation: Reluctance is the opposition offered by a magnetic path to the establishment of flux, just as resistance opposes electric current.

• A. E.m.f.
• B. Current
• C. Current density
• D. Conductivity

Explanation: Magnetic flux plays the same circuit-flow role as electric current. Magnetomotive force corresponds to voltage, while reluctance…

• A. weber
• B. weber/sq. m
• C. ampere turn/meter
• D. ampere turn

Explanation: Retentivity is the residual flux density left when the magnetising force is removed.

• A. permeance
• B. reluctance
• C. flux
• D. inductance

Explanation: Conductance is the reciprocal of electrical resistance, while permeance is the reciprocal of magnetic reluctance.

• A. retentivity
• B. resistivity
• C. permeability
• D. inductance

Explanation: Conductivity measures how readily electric flux or current passes through a material, while permeability measures how readily magnetic…

• A. time constant remains unchanged
• B. initial rate of rise of current is doubled
• C. final steady current is doubled
• D. time constant is halved

Explanation: For an RL circuit, the time constant is τ = L/R. Doubling both L and R leaves L/R unchanged, although the initial current slope and final…

• A. 25
• B. 50
• C. 41.4
• D. 100

Explanation: The energy stored in a coil is W = ½LI², so doubling the energy requires the current to become √2 times its original value.