Free Circuit Analysis MCQs with Answers

• A. Square wave
• B. Sine wave
• C. Half wave rectified sine wave
• D. Triangular wave

Explanation: Peak factor is peak value divided by RMS value. A half-wave rectified sine wave has RMS value Iₘ/2, so its peak factor is 2, greater than…

• A. increasing core length
• B. decreasing the number of turns
• C. decreasing the diameter of the former
• D. choosing core material having high relative permeability

Explanation: For a coil, L = μN²A/l, so using a core with higher relative permeability increases inductance.

• A. Vc and VR
• B. VL and VR
• C. Vc and VL
• D. none of the above

Explanation: In a series AC circuit, the inductor voltage leads current by 90° and the capacitor voltage lags by 90°, making V_L and V_C 180° out of…

• A. 0.5 of peak value
• B. 0.707 of peak value
• C. same as peak value
• D. zero

Explanation: A sinusoidal waveform, whether sine or cosine, has RMS value equal to its peak value divided by √2.

• A. series resistance needs a low-resistance source for sharp rise in current
• B. series resonance needs a high-resistance source for sharp increase in current
• C. parallel resonance needs a low-resistance source for a sharp in¬crease in impedance
• D. parallel resonance needs a low-resistance source for a sharp rise in line current

Explanation: At series resonance, a low source resistance allows the circuit current to rise sharply because the net reactance is zero.

• A. the speed with which the alternator runs
• B. the number of cycles generated in one minute
• C. the number of waves passing through a point in one second
• D. the number of electrons passing through a point in one second

Explanation: Frequency is the number of complete cycles occurring each second, measured in hertz.

• A. inductive reactance
• B. capacitive reactance
• C. resistance
• D. capacitance

Explanation: Resistance, inductive reactance, and capacitive reactance are all measured in ohms.

• A. less than unity
• B. unity
• C. greater than unity
• D. zero

Explanation: In a steady-state D.C. circuit, voltage and current have no phase difference, so cos φ = cos 0° = 1. Thus the power factor is unity.

• A. be reduced by half
• B. be doubled
• C. be four times as high
• D. be reduced to one fourth

Explanation: For a pure inductor, Xₗ = 2πfL and I = V/Xₗ, so current is inversely proportional to frequency.

• A. be reduced by half
• B. be doubled
• C. be four times at high
• D. be reduced to one fourth

Explanation: For a pure capacitor, Xc = 1/(2πfC), so halving frequency doubles the capacitive reactance. Since I = V/Xc, the current is reduced by half.

• A. the current through the resistance is more
• B. the current through the resistance is less
• C. both resistance and inductance carry equal currents
• D. none of the above

Explanation: Both branches have the same applied voltage and equal impedance magnitudes of 3.5 Ω.

• A. true power
• B. reactive power
• C. volt-amperes
• D. instantaneous power

Explanation: Apparent power is S = VI, and multiplying it by cos φ gives VI cos φ. This is the true or active power consumed by the circuit.

• A. the capacitive reactance in ohms
• B. the current flowing in capacitor
• C. the size of the capacitor being quite big
• D. the statement is incorrect

Explanation: An ideal pure capacitor has a 90° phase angle, so its average power is VI cos 90° = 0 W.

• A. apparent power
• B. true power
• C. reactive power
• D. none of the above

Explanation: In a pure resistance, voltage and current are in phase, so all supplied power is converted into heat.

• A. zero
• B. 0.08 lagging
• C. 0.8 leading
• D. unity

Explanation: At parallel R-L-C resonance, the inductive and capacitive susceptances cancel, leaving the supply current in phase with the voltage.

• A. the current is in phase with the voltage
• B. the current lags behind the voltage by 90°
• C. the current leads the voltage by 90°
• D. the current can lead or lag by 90°

Explanation: In a pure inductive circuit, current lags voltage by 90° because the inductor opposes changes in current.

• A. unsymmetrical part of the wave form
• B. the quarter cycle
• C. the half cycle
• D. the whole cycle

Explanation: For an unsymmetrical AC waveform, positive and negative portions are not equal, so averaging over a half-cycle can give a misleading…

• A. changes in the stored energy in the inductors and capacitors
• B. impedance of the circuit
• C. applied voltage to the circuit
• D. resistance of the circuit

Explanation: Transient current appears when the energy stored in inductors or capacitors changes during switching or circuit adjustment.

• A. current lags behind the voltage by 90°
• B. current leads the voltage by 90°
• C. current can lead or lag the voltage by 90°
• D. current is in phase with the voltage

Explanation: Ohm's law gives i = v/R for a pure resistor, so voltage and current reach their peaks and zero crossings together.

• A. C only
• B. L only
• C. R only
• D. all above

Explanation: An ideal resistor converts electrical energy into heat, producing real power loss.