DC and AC Circuit Analysis Flashcards

In a series RLC circuit at resonance, what happens to the impedance?

Answer: Impedance equals resistance R

At resonance, inductive and capacitive reactances cancel, leaving only the resistance R as the total impedance.

A delta-connected load has each branch impedance of 30 Ω. What is the equivalent wye impedance per phase?

Answer: 10 Ω

For delta-to-wye conversion, Z_Y = Z_Δ / 3, so 30/3 = 10 Ω.

What does the time constant τ represent in an RC circuit?

Answer: Time for voltage to reach 63.2% of its final value

The time constant τ = RC is the time required for the capacitor voltage to rise to approximately 63.2% (1 - 1/e) of the source voltage.

Using mesh analysis, what is the primary variable solved for?

Answer: Mesh currents

Mesh analysis assigns a loop current to each independent mesh and solves for those mesh currents using KVL equations.

In a purely inductive AC circuit, what is the phase relationship between voltage and current?

Answer: Voltage leads current by 90°

In a pure inductor, the induced EMF (voltage) leads the current by 90° due to the inductor's opposition to current change.

A circuit has a power factor of 0.8 lagging. What angle does this correspond to?

Answer: 36.87°

Power factor = cos(θ), so θ = arccos(0.8) ≈ 36.87°, and lagging indicates an inductive circuit.

Which theorem states that a linear two-terminal network can be replaced by a single voltage source in series with a single impedance?

Answer: Thevenin's theorem

Thevenin's theorem replaces any linear network with an equivalent Vth in series with Zth as seen from the output terminals.