Shown below are some of the formulas for power used to calculate power in electronic circuitry.
pertains to the rate at which work is being done. Work is done whenever a
force causes motion. The instantaneous rate at which work is done is
called the electric power rate and is measured in WATTS.
Electric power is transformed to other forms of power when electric charges move through an electric potential (voltage) difference. When an electric charge moves through a potential difference, from a high voltage to a low voltage, the potential does work on the charges, converting the energy in the potential to kinetic energy of the charges, or some other form. This occurs in most electrical appliances, such as light bulbs, electric motors, and heaters; they consume electric power, converting it to mechanical work, heat, light, etc. In electronics these are called passive devices.
If the charges are forced to move by an outside force in the direction from a lower potential to a higher, power is transferred to the electric current. This occurs in sources of electric current, such as electric generators and batteries.
Formulas for power in dc circuits are:
For ac circuits:
True power is measured in watts:
Another way to calculate reactive power is:
Subtract the smaller from the larger:
In electronics, which deals with more passive than active devices, electric power consumed in a device is defined to have a positive sign, while power produced by a device is defined to have a negative sign. This is called the passive sign convention.
In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power (also referred to as active power). That portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power.
You can find more detailed information about power in NEETS, Module 2, Introduction to Alternating Current and Transformers.