Free Circuit Analysis MCQs with Answers

• A. 25% of maximum value
• B. 50% of maximum value
• C. 63% of maximum value
• D. 90% of the maximum value

Explanation: For a first-order circuit, the response reaches 1 − e⁻¹ = 0.632 of its final value after one time constant, or about 63%.

• A. power is consumed in resistance and is equal to I R
• B. exchange of power takes place between inductor and supply line
• C. exchange of power takes place between capacitor and supply line
• D. exchange of power does not take place between resistance and the supply line
• E. all above are correct

Explanation: The resistor absorbs real power I²R, while the inductor and capacitor exchange reactive power with the source and each other; an ideal…

• A. 42.42 sin 3141
• B. 60 sin 25 t
• C. 30 sin 50 t
• D. 84.84 sin 25 t

Explanation: A 30 A rms sinusoid has peak value 30√2 = 42.42 A, and its angular frequency is 2π(50) = 314 rad/s.

• A. low efficiency
• B. high power factor
• C. unity power factor
• D. maximum load current

Explanation: Since kVAR/kW = tanφ, a small reactive-power component compared with real power means a small phase angle and hence a high power factor.

• A. 12 kW
• B. 22 kW
• C. 32 kW
• D. 64 kW

Explanation: Real power is P = S cosφ, so P = 40 kVA × 0.8 = 32 kW. The lagging nature affects current phase, not this real-power multiplication.

• A. the big size of the inductor
• B. the reactance of the inductor
• C. the current flowing in the inductor
• D. the statement given is false

Explanation: An ideal pure inductor has zero average real power because voltage and current differ by 90°, so energy is returned to the source each…

• A. demand
• B. load
• C. power
• D. form

Explanation: Power factor is the ratio of active power to apparent power, expressed as kW/kVA or cos φ.

• A. 4 kVAR
• B. 6 kVAR
• C. 8 kVAR
• D. 16 kVAR

Explanation: Using the power triangle, reactive power is Q = √(S² − P²) = √(10² − 8²) = 6 kVAR.

• A. have a high voltage developed across each inductive and capacitive section
• B. have a high impedance
• C. act like a resistor of low value
• D. have current in each section equal to the line current

Explanation: At parallel resonance, inductive and capacitive branch currents largely cancel at the supply, so the circuit presents a high impedance.

• A. ratio of net reactance and impedance
• B. ratio of kW and kVA
• C. ratio of J and Z
• D. ratio of W and VA

Explanation: Power factor is kW/kVA or W/VA, equivalently the ratio of the resistance to impedance in a series R-L-C circuit.

• A. a line which represents the magnitude and phase of an alternating quantity
• B. a line representing the magnitude and direction of an alternating quantity
• C. a coloured tag or band for distinction between different phases of a 3-phase supply
• D. an instrument used for measuring phases of an unbalanced 3-phase load

Explanation: A phasor is a rotating-vector representation of a sinusoidal quantity, showing both its magnitude and phase angle.

• A. reactive power in a circuit
• B. the extent of neutralisation of reactive power in a circuit
• C. a purely capacitive circuit's ability to pass current
• D. a purely capacitive circuit's ability to resist the flow of current

Explanation: Capacitive susceptance is the imaginary part of admittance, with magnitude B = ωC, and indicates how readily a capacitor passes…

• A. 0°
• B. 45°
• C. 90°
• D. 180°

Explanation: For equal-frequency sinusoidal waves, a maximum of one wave coincides with a zero crossing of the other when their phase difference is…

• A. lags
• B. leads
• C. remains in phase with
• D. none of the above

Explanation: In a parallel R-C circuit, the resistor current is in phase with voltage while the capacitor current leads it by 90°, so their total…

• A. The current through each element is same
• B. The voltage across element is in proportion to it's resistance value
• C. The equivalent resistance is greater than any one of the resistors
• D. The current through any one element is less than the source current

Explanation: In a parallel circuit, source current divides among the branches, so the current in any one branch is less than the total source current.

• A. between 0° and 90°
• B. between 90° and 180°
• C. between 180° and 270°
• D. no where

Explanation: The slope of a sine wave is its derivative, a cosine function, so it changes continuously rather than remaining constant over any listed…

• A. resistance only
• B. inductance only
• C. capacitance only
• D. none of the above

Explanation: Average AC power is dissipated in resistance, where energy is converted into heat.

• A. resistive
• B. inductive
• C. capacitive
• D. none of the above

Explanation: At very low frequency, capacitive reactance Xc = 1/(2πfC) becomes very large, so a series R-C circuit is dominated by its capacitive…

• A. high voltage across the load
• B. low voltage across the load
• C. unequal line voltages across the load
• D. minimun voltage across the load

Explanation: With the neutral floating, unequal phase impedances cannot maintain their intended phase-to-neutral voltages, so the neutral point shifts…

• A. 282.8 V
• B. 141.4 V
• C. 111 V
• D. 100 V

Explanation: For a half-wave rectified sine wave, the RMS value is Iₘ/2, while for a full-wave rectified sine wave it is Iₘ/√2.