Basic AC Theory

In a circuit consisting of a resistor connected to an AC supply, the current

• leads the voltage
• lags the voltage
• is in phase with the voltage
• depends on the source of voltage

A capacitor is connected to an AC voltage. As the frequency of the voltage increases, the capacitive reactance

• increases
• decreases
• remains the same
• depends on the direction of current

The frequency of an alternating electrical system is measured in

• cycles

• volts

• hertz

• seconds

A phasor is

• part of a three-phase system

• a method of representing a sinusoidally varying system

• the angle between alternating current and voltage

• always measured in radians

The effect which limits current flow in a pure inductor connected to an

alternating-voltage supply is called the

• induced EMF

• inductive reactance

• capacitive reactance

• resistance

If a supply at 230V, 50Hz is connected to a 420mH inductor, the current

flow will be

• 1.74 A

• 0.57 A

• 11.4 A

• 31.6 μA

If a sinusoidal voltage is applied to a pure capacitor

• the average current flow will be zero

• the current will lead the voltage by 90⁰

• the current will lag the voltage by 90⁰

• current and voltage will be in phase

An alternating supply of 12V at 1kHz is connected to a capacitor, and

the current is found to be 15mA. The capacitance of the capacitor is

• 800 Ω

• 625 nF

• 50.3 μF

• 198 nF

The opposition to current flow in an AC resistive circuit is called:

• resistance

• inductance

• reactance

• impedance

The opposition to current flow in an AC capacitive or inductive current is

called:

• resistance

• inductance

• reactance

• impedance