What is Electric Power?

Before reading about electric power it is essential to have a basic idea about power. The word power is a little tricky to understand. Consider that you are riding a bicycle at a speed of 20km/hr for an hour. A certain amount of work is done by you here. The amount of work done by you every second is known as power. Hence, power is the amount of work done per unit time.

power equation

The unit of power is watts, which is equal to 1 Joules/second.

Electric power

Now consider that you are driving an electric car at a velocity of 100km/hr for an hour. An electric car basically consists of an electric motor. A certain amount of work is done by this motor during this displacement. An electric motor is a device that converts electric energy into mechanical energy. Hence the amount of electric energy converted by the motor every second is known as the Electric power consumed by the motor.

Definition of Electric power

All electric devices convert electric energy into any other forms of energy such as mechanical energy, heat, light etc. or vice versa. Hence electric power can be defined as follows:

Electric power can be defined as the amount of power consumed by or generated by an electric or electronic device. It depends on the applied or generated voltage and the current flow.

Power = Current x Voltage

Unit of electric power

Electric power is expressed in watts or kilowatts. Normally the terms wattage is used to denote the power consumed by an electric load. All electric and electronic appliances at your home have their power consumption mentioned on them in terms of watts. In countries following NEMA standards, electric power is rated in horsepowers.

One Horsepower = 746 watts = 0.746 kilowatt

Mathematical expressions

Electric power can be expressed in terms of voltage (V), current (I) and resistance (R). The following are the mathematical expressions for DC power calculations:

DC Power formulae

AC Power

Ac power is normally calculated based on the RMS value of AC voltage and current. It depends on the power factor of the load. AC power is described by the following terms: Real power, reactive power and apparent power. The real power is expressed in kilowatts, reactive power is expressed in kilo-volt-ampere reactance (kVAR) and apparent power is expressed in volt-amperes or kilo-volt-amperes (VA or kVA). The formulae for the calculation of each term are given below:

AC power formulae

Power Dissipation

Power dissipation is the term normally used to denote the power lost by a device or circuit in the form of heat. It depends upon the resistance offered by the device to the current flow. The Power dissipated across a device is directly proportional to the ohmic value of the device and the square of current flowing through it.

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