# Overview of electrical power

### - a tutorial, overview or summary of electrical power and the unit of electrical power - the Watt.

Voltage is one of the fundamental parameters associated with any electrical or electronic circuit. It is seen widely in specifications of a host of electrical items from batteries to radios and light bulbs to shavers.

## Potential difference

The electrical potential or voltage is a measure of the electrical pressure available to force the current around a circuit. In the comparison of a water system mentioned when describing current, the potential can be likened to the water pressure at a given point. The greater the pressure difference across a section of the system, the greater the amount of water which will flow. Similarly the greater the potential difference or voltage across a section of an electrical circuit, the greater the current which will flow.

## Units of voltage

The basic unit of voltage is the volt, named after the Italian scientist, Alessandro Volta, who made some early batteries and performed many other experiments with electricity.

To give an idea of the voltages which are likely to be encountered, a CB radio will usually operate from a supply of around 12 volts (12 V). The cells used in domestic batteries have a voltage of around 1.5 volts. Rechargeable Nickel Cadmium cells have a slightly smaller voltage of 1.2 volts, but can normally be used interchangeably with the non-rechargeable types.

In other areas voltages much smaller and much greater than this can be encountered. The signal input to an audio amplifier will be smaller than this, and the voltages will often be measured in millivolts (mV) or thousandths of a volt. The signals at the input to a radio are even smaller than this and will often be measured in microvolts (?V) or millionths of a volt.

At the other extreme much greater voltages may be heard about. The cathode ray tubes in a television or computer monitors require voltages of several kilovolts (kV) or thousands of volts, and even larger voltages of millions of volts or megavolts (MV) may be heard of in conjunction with topics like lightning.

## EMF and PD

The voltage for a battery or single cell is stated as a voltage. However it is found that when the battery is in use its voltage will fall, especially as it becomes older and it has been used. The reason for this is that there is some resistance inside the cell. As current flows a voltage drop forms across this and the voltage seen at the output is less than expected. Even so the voltage seen at the terminals if the battery was not supplying current would still be the same. This no load voltage is known as the electro-motive force (EMF), and is the internal voltage which is generated by the cell, or other source of power.

More Basic Concepts:
Voltage     Current     Resistance     Capacitance     Power     Transformers     RF noise     Decibel, dB     Q, quality factor