The correct answer is: A. Less than unity.
A power factor is a dimensionless number that measures how efficiently electrical energy is being used in a circuit. A power factor of 1 indicates that all of the electrical energy is being used, while a power factor of less than 1 indicates that some of the electrical energy is being wasted.
In a DC circuit, there is no reactive power, so the power factor is always less than unity. This is because the current and voltage are always in phase in a DC circuit, so there is no phase angle difference between them.
In an AC circuit, there can be both active and reactive power. The active power is the power that is used to do work, while the reactive power is the power that is used to store and release energy in the circuit’s inductance and capacitance. The power factor of an AC circuit is the ratio of the active power to the apparent power. The apparent power is the product of the current and voltage, and it is always greater than or equal to the active power.
The power factor of an AC circuit can be improved by using capacitors or inductors to cancel out the reactive power. This is called power factor correction.
Here is a brief explanation of each option:
- Option A: Less than unity. This is the correct answer. The power factor of a DC circuit is always less than unity.
- Option B: Unity. This is not the correct answer. The power factor of a DC circuit is never unity.
- Option C: Greater than unity. This is not the correct answer. The power factor of a DC circuit is never greater than unity.
- Option D: Zero. This is not the correct answer. The power factor of a DC circuit is never zero.