AC Circuits - Part 1

What does the phase angle φ in an AC circuit determine?

• The amplitude of the current and voltage

• The frequency of the current and voltage

• Which of the two quantities (current or voltage) leads or lags

• The resistance in the circuit

When φ > 0, what is the relationship between the current and voltage in an AC circuit?

• The current leads the voltage

• The voltage leads the current

• The current and voltage are in phase

• The current and voltage are completely out of phase

What happens when φ = π/2 in an AC circuit?

• The current and voltage are in phase

• The current leads the voltage by half a period

• The current and voltage are completely out of phase

• One signal leads/lags the other by a quarter of a period

According to Ohm's law, how is the voltage across a resistor related to the current and resistance?

• V_R(t) = i(t) / R

• V_R(t) = i(t)R

• V_R(t) = i(t) + R

• V_R(t) = i(t) - R

What is the phase relationship between voltage and current in a resistor?

• The voltage leads the current by a quarter of a period.

• The voltage and current are out of phase.

• The voltage and current are in phase.

• The voltage lags the current by a quarter of a period.

What is the expression for the voltage across an inductor in terms of inductive reactance X_L?

• V_L(t) = V_L cos(ωt + π/2) with V_L = I/X_L

• V_L(t) = V_L cos(ωt) with V_L = IX_L

• V_L(t) = V_L cos(ωt + π/2) with V_L = IX_L

• V_L(t) = V_L sin(ωt) with V_L = I/X_L

What is the relationship between the charge on the plates of a capacitor and the voltage across it?

• V_C(t) = q(t)C

• V_C(t) = q(t) / C

• V_C(t) = C / q(t)

• V_C(t) = q(t) + C

What is the expression for capacitive reactance X_C?

• X_C = 1/(Lω)

• X_C = 1/(Cω)

• X_C = Lω

• X_C = Cω

What is the relationship between the voltage across a capacitor v_C(t) and the current i(t) in terms of phase?

• v_C(t) = V_C cos(ωt)

• v_C(t) = V_C cos(ωt + π/2)

• v_C(t) = V_C sin(ωt)

• v_C(t) = V_C cos(ωt - π/2)

If V_C = I X_C, what does V_C represent in terms of I and X_C?

• The voltage across the inductor

• The voltage across the resistor

• The voltage across the capacitor

• The current through the resistor