Topic 6(ii): Alternating Current

In an RC, RL or RCL circuit, the total opposition to alternating current is called as

• Reactant

• Impedence

• Phase angle

• Resistance

Based on the phasor diagram of RL circuit. The rms supply voltage V (or total voltage) of the circuit is given by

• The sum of all voltage in the circuit.

• The sum of the squares of voltage across R and L

• The square root of the sum of the squares of the voltage across R and L,

• The square root of the sum of all voltage in the circuit

At resonance frequency...

• Impedence is minimum, rms current flow is maximum

• Impedence is maximum, rms current flow is minimum

• Impedene is zero, rms current flow is maximum

• Impedence is increasing, rms current flow is decreasing

Choose the wrong statement about the power of an ac circuit

• There are no power dissipated in capacitor and inductor

• power is only dissipated in resistor

• the ratio of real power to apparent power is called the power factor

• At resonance, power factor is equal to real power

Instantaneous power is defined as

• the product of instantaneous current and voltage

• the product of rms current and voltage

• the product of peak current and voltage

• specific power

An alternating current I in amperes varies with time t in seconds as I=2 sin 300πt. The rms value of the current in A and the frequency f in Hz are

• Irms=1.4 A, f=100 Hz

• Irms=1.4 A, f=150 Hz

• Irms=2 A, f=250 Hz

• Irms=2 A, f=300 Hz