Circuit Theory Flashcards

In a delta-connected three-phase load, the relationship between line current and phase current is:

Answer: IL = √3 × IP

In a delta connection, IL = √3 × IP because each line carries the phasor sum of two phase currents displaced by 60°.

The bandwidth (BW) of a series resonant circuit is related to its Q-factor and resonant frequency (f₀) by:

Answer: BW = f₀ / Q

Bandwidth BW = f₀/Q; a higher Q-factor produces a narrower bandwidth and sharper selectivity.

When two inductors are magnetically coupled with a mutual inductance M, the total inductance when connected series-aiding is:

Answer: L1 + L2 + 2M

For series-aiding coupled inductors, LT = L1 + L2 + 2M, because the mutual inductance adds to both coils.

A wattmeter in an AC circuit measures:

Answer: True (real) power (W)

A wattmeter measures true (real) power in watts, which accounts for the phase angle between voltage and current.

Applying mesh analysis, a mesh current is assumed to flow:

Answer: Around a closed loop (mesh) in one direction

In mesh analysis, a mesh current is assigned to each independent closed loop (mesh) and is assumed to circulate around that loop.

A capacitor fully charged to 100V is discharged through a 1 MΩ resistor. The RC time constant is 2 seconds. After one time constant, the voltage is approximately:

Answer: 36.8V

After one time constant, the voltage decays to V₀ × e⁻¹ ≈ 100 × 0.368 = 36.8V.

Apparent power (S) in an AC circuit is the vector sum of real power (P) and reactive power (Q). The correct relationship is:

Answer: S = √(P² + Q²)

Apparent power S = √(P² + Q²), forming the hypotenuse of the power triangle with real and reactive power as legs.