Question

What is meant by the wattless component of the current?

Answer 1

You can start by describing the general equation for power, i.e. $P = VI$ . Then explain how power consumed is measured when we are dealing with DC. Then move to explain how the average power consumed in a full cycle of AC is zero (this AC is called wattless current)

Complete Step-by-Step solution:
We know that when current flows through a circuit, a certain value of power is consumed. It is given by the following equation
$P = VI$
Here, $P =$ Power
$V =$ Voltage
$I =$ Current
When we apply a DC on the circuit the value of power can be simply calculated by using the equation for power stated above.
But, when we apply an AC on the circuit the situation becomes different. We know in alternating current the current reverses its direction after certain fixed intervals. So if we suppose that the power for the first half cycle is $P$ , then the power for the next half-cycle becomes $- P$ (as the magnitude of voltage and current remains the same, but the direction of the current is reversed). Now if we calculate the total power for a full cycle ( ${P_T}$ ), we get
${P_T} = P - P$
${P_T} = 0$
The average power consumed is zero when AC runs through a circuit.
Wattless current – The current in an AC circuit is called Wattless when the average power consumed in such a circuit is zero. It is also known as idle current.
As we know the power in a circuit is measured in “watts” which is zero, in this case, hence it is termed as wattless current.

Note: We discussed how the power consumption for a full cycle is zero. But it is very important to remember that in reality, it does not mean that by using AC no power is consumed, it just means it should theoretically not consume any power. In reality, some energy is dissipated as heat and sound energy.