AC Circuits and Power Factor MCQs 2026

Inductive reactance XL equals

1. A 1/(2 pi f L) ✓
2. B 2 pi f C ✓
3. C L/f ✓
4. D 2 pi f L ✓

Capacitive reactance XC equals

1. A 2 pi f C ✓
2. B 2 pi f L ✓
3. C C/f ✓
4. D 1/(2 pi f C) ✓

At series resonance, impedance is

1. A maximum and infinite ✓
2. B minimum and equals R ✓
3. C zero always ✓
4. D purely capacitive always ✓

Series resonant frequency is

1. A 2 pi sqrt(LC) ✓
2. B 1/(LC) ✓
3. C 1/(2 pi sqrt(LC)) ✓
4. D sqrt(L/C) ✓

Power factor is defined as

1. A cos phi (ratio of real to apparent power) ✓
2. B sin phi ✓
3. C tan phi only ✓
4. D S/P always ✓

Apparent power S in AC circuit equals

1. A V I cos phi only ✓
2. B V I sin phi only ✓
3. C V I ✓
4. D I squared R only ✓

Active (real) power P equals

1. A V I sin phi ✓
2. B V I only ✓
3. C I squared L ✓
4. D V I cos phi ✓

Reactive power Q equals

1. A V I cos phi ✓
2. B V I sin phi ✓
3. C V I only ✓
4. D V squared C ✓

Phasor representation of AC voltage uses

1. A rotating vector with magnitude and phase angle ✓
2. B scalar DC value only ✓
3. C binary digits only ✓
4. D magnetic flux density only ✓

RMS value of sinusoidal voltage Vmax is

1. A Vmax/sqrt(2) ✓
2. B Vmax times 2 ✓
3. C Vmax squared ✓
4. D Vmax/2 ✓

Average power in AC consumed by resistor depends on

1. A peak values only without cos phi ✓
2. B frequency only ✓
3. C reactive power only ✓
4. D RMS voltage and RMS current and cos phi ✓

A lagging power factor indicates

1. A inductive load (current lags voltage) ✓
2. B capacitive load ✓
3. C purely resistive load ✓
4. D zero current ✓

A leading power factor indicates

1. A capacitive load (current leads voltage) ✓
2. B inductive load ✓
3. C purely resistive load ✓
4. D infinite reactance ✓

XL at f=50 Hz, L=0.1 H is approximately

1. A 314.2 ohm ✓
2. B 3.14 ohm ✓
3. C 0.314 ohm ✓
4. D 31.4 ohm ✓

XL at f=60 Hz, L=0.05 H is approximately

1. A 188.5 ohm ✓
2. B 1.885 ohm ✓
3. C 18.85 ohm ✓
4. D 0.188 ohm ✓

XL at f=100 Hz, L=0.02 H is approximately

1. A 125.7 ohm ✓
2. B 12.56 ohm ✓
3. C 1.256 ohm ✓
4. D 0.125 ohm ✓

XL at f=50 Hz, L=0.2 H is approximately

1. A 628.3 ohm ✓
2. B 6.28 ohm ✓
3. C 0.628 ohm ✓
4. D 62.8 ohm ✓

XL at f=400 Hz, L=0.01 H is approximately

1. A 251.3 ohm ✓
2. B 2.51 ohm ✓
3. C 0.251 ohm ✓
4. D 25.1 ohm ✓

XC at f=50 Hz, C=0.0001 F is approximately

1. A 318 ohm ✓
2. B 3.18 ohm ✓
3. C 0.318 ohm ✓
4. D 31.8 ohm ✓

XC at f=60 Hz, C=0.00005 F is approximately

1. A 531 ohm ✓
2. B 53.1 ohm ✓
3. C 5.31 ohm ✓
4. D 0.531 ohm ✓

XC at f=100 Hz, C=0.00001 F is approximately

1. A 1590 ohm ✓
2. B 15.9 ohm ✓
3. C 1.59 ohm ✓
4. D 159 ohm ✓

XC at f=50 Hz, C=0.0002 F is approximately

1. A 15.9 ohm ✓
2. B 159 ohm ✓
3. C 1.59 ohm ✓
4. D 0.159 ohm ✓

XC at f=60 Hz, C=0.00008 F is approximately

1. A 33.2 ohm ✓
2. B 332 ohm ✓
3. C 3.32 ohm ✓
4. D 0.332 ohm ✓

If P=100 W and phi=45 deg with same V I, power factor is

1. A 0.29 ✓
2. B 0.707 ✓
3. C 1.41 ✓
4. D 0.71 ✓

In AC, impedance Z general form is

1. A R only always ✓
2. B R + jX (resistance plus reactance) ✓
3. C X only always ✓
4. D V/I without phase ✓

Capacitor in AC passes

1. A DC readily ✓
2. B zero AC always ✓
3. C higher frequency more easily ✓
4. D only reactive power never ✓

Inductor in AC opposes

1. A voltage always zero ✓
2. B DC strongly ✓
3. C change of current (higher Z at higher f) ✓
4. D power factor unity always ✓

Resonance in series RLC occurs when

1. A R equals L ✓
2. B C equals zero ✓
3. C XL equals XC ✓
4. D P equals Q ✓

Bandwidth of series resonant circuit relates to Q as

1. A BW = fr/Q approximately ✓
2. B BW = Q/fr only ✓
3. C BW = fr times Q squared ✓
4. D BW independent of R ✓

Power triangle shows

1. A only DC resistance ✓
2. B only flux linkage ✓
3. C S as hypotenuse, P and Q as legs ✓
4. D only back EMF ✓

Correction of lagging PF uses

1. A series inductors ✓
2. B more resistors only ✓
3. C capacitors in parallel with load ✓
4. D short circuit ✓

Form factor of sine wave is

1. A 0.707 ✓
2. B 1.414 ✓
3. C 2.0 ✓
4. D 1.11 (RMS/mean for half cycle context) ✓

Crest factor of sine wave is

1. A 1 ✓
2. B sqrt(2) (peak/RMS) ✓
3. C 0.5 ✓
4. D 2 ✓

Instantaneous power in pure inductor averages to

1. A maximum real power ✓
2. B VI always ✓
3. C zero over a full cycle ✓
4. D V squared/R ✓

Skin effect causes AC current to

1. A concentrate near conductor surface at high frequency ✓
2. B uniform across area always ✓
3. C flow only in core ✓
4. D stop entirely ✓

Two wattmeter method measures power in

1. A DC motors only ✓
2. B single capacitor only ✓
3. C magnetic circuits only ✓
4. D three-phase circuits ✓

In pure capacitor, current

1. A lags by 90 ✓
2. B leads voltage by 90 degrees ✓
3. C in phase ✓
4. D opposite by 180 always ✓

In pure inductor, current

1. A lags voltage by 90 degrees ✓
2. B leads by 90 ✓
3. C in phase ✓
4. D zero always ✓

Admittance Y is

1. A same as impedance ✓
2. B R times X ✓
3. C reciprocal of impedance (1/Z) ✓
4. D power factor ✓

Susceptance B is

1. A real part of Z ✓
2. B imaginary part of admittance ✓
3. C power in watts ✓
4. D flux in weber ✓

Parallel R-L branch admittance magnitude uses

1. A G plus B only ✓
2. B sqrt(G² + B²) ✓
3. C G minus B only ✓
4. D R plus XL ✓

Complex power S is

1. A P only ✓
2. B Q only ✓
3. C P + jQ ✓
4. D V/I angle only ✓

At unity PF, reactive power Q equals

1. A maximum ✓
2. B zero ✓
3. C equal to S ✓
4. D equal to P ✓

Ferromagnetic core in inductor

1. A eliminates reactance ✓
2. B increases inductance and can introduce losses ✓
3. C blocks DC only ✓
4. D makes PF always unity ✓

R=6 ohm, X=8 ohm in series: |Z| is

1. A 14 ohm ✓
2. B 2 ohm ✓
3. C 48 ohm ✓
4. D 10 ohm ✓

Phase angle phi for R-L series circuit is

1. A tan inverse (R/XL) ✓
2. B zero always ✓
3. C tan inverse (XL/R) ✓
4. D 90 degrees always ✓

Phase angle for R-C series circuit is

1. A tan inverse (XC/R) leading ✓
2. B tan inverse (R/XC) lagging ✓
3. C zero always ✓
4. D 180 degrees ✓

R=3 ohm, X=4 ohm in series: |Z| is

1. A 7 ohm ✓
2. B 5 ohm ✓
3. C 1 ohm ✓
4. D 12 ohm ✓

In parallel resonance, impedance is

1. A minimum ✓
2. B zero ✓
3. C equal to R always ✓
4. D maximum ✓

An R-L series circuit has impedance

1. A sqrt(R squared + XL squared) ✓
2. B R plus XL always ✓
3. C R minus XL ✓
4. D XL only ✓

R=5 ohm, X=12 ohm in series: |Z| is

1. A 17 ohm ✓
2. B 7 ohm ✓
3. C 13 ohm ✓
4. D 60 ohm ✓

An R-C series circuit has impedance

1. A R plus XC always ✓
2. B R minus XC ✓
3. C XC only ✓
4. D sqrt(R squared + XC squared) ✓

Quality factor Q of series RLC at resonance is

1. A R/omega L ✓
2. B omega C R ✓
3. C omega L / R (or 1/(omega C R)) ✓
4. D L/C only ✓

In a purely resistive AC circuit, power factor is

1. A zero ✓
2. B leading ✓
3. C lagging always ✓
4. D unity (1) ✓

R=7 ohm, X=24 ohm in series: |Z| is

1. A 25 ohm ✓
2. B 31 ohm ✓
3. C 17 ohm ✓
4. D 168 ohm ✓

R=9 ohm, X=40 ohm in series: |Z| is

1. A 49 ohm ✓
2. B 31 ohm ✓
3. C 41 ohm ✓
4. D 360 ohm ✓