  Electronics >> Basics of Electronics >> Power

## Definition of Power

Some of the definition of power are:

1. Electrical power: The product of voltage and current.
2. Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.
3. Electric energy produced per unit time.

Current flowing through a poor conductor produces heat by an effect similar to mechanical friction. That heat represents energy that comes from the charge traveling across the voltage difference. Remember that separated charges have the potential to do work and provide energy. The work involved in heating a resistor is not very useful, unless we are making a hotplate; rather it is a byproduct of restricting the current flow. Power is measured in units of watts (W), named after James Watt, the Englishman who invented the steam engine, a device for producing lots of useful power.

## How to Calculate Power?

The power that is released into the resistor as heat can be calculated as P=VI , where I is the current flowing through the resistor and V is the voltage across it.

Ohm's law relates these two quantities, so we can also calculate the power as The power produced in a resistor raises its temperature and can change its value or destroy it.

Most resistors are air-cooled and they are made with different power handling capacity. The most common values are 1/8, 1/4, 1, and 2 watt resistors, and the bigger the wattage rating, the bigger the resistor physically.

Some high power applications use special water cooled resistors. Most of the resistors on the RoboBoard are 1/8 watt.