An accumulation of electrostatic charge, such as an excess or shortage of electrons, is always associated with a voltage. There are other situations in which voltages exist. Voltage can be generated at a power plant, produced in an electrochemical reaction, or caused by light rays striking a semiconductor chip. It can be produced when an object is moved in a magnetic field, or is placed in a fluctuating magnetic field.
A potential difference between two points produces an electric field, represented by electric lines of flux in following figure.
Electric lines of flux always exist near poles of electric charge.
There is a pole that is relatively positive, with fewer electrons, and one that is relatively negative, with more electrons. The positive pole does not necessarily have a deficiency of electrons compared with neutral objects, and the negative pole does not always have a surplus of electrons relative to neutral objects. But the negative pole always has more electrons than the positive pole.
The abbreviation for volt (or volts) is V. Sometimes, smaller units are used. The millivolt (mV) is equal to a thousandth (0.001) of a volt. The microvolt (μV) is equal to a millionth (0.000001) of a volt. It is sometimes necessary to use units larger than the volt. One kilovolt (kV) is one thousand volts (1000 V). One megavolt (MV) is 1 million volts (1,000,000 V) or one thousand kilovolts (1000 kV).
In a dry cell, the voltage is usually between 1.2 and 1.7 V; in a car battery, it is 12 to 14 V. In household utility wiring, it is a low-frequency alternating current of about 117 V for electric lights and most appliances, and 234 V for a washing machine, dryer, oven, or stove. In television sets, transformers convert 117 V to around 450 V for the operation of the picture tube. In some broadcast transmitters, the voltage can be several kilovolts.
The largest voltages on our planet occur between clouds, or between clouds and the ground, in thundershowers. This potential difference can build up to several tens of megavolts. The existence of a voltage always means that charge carriers, which are electrons in a conventional circuit, flow between two points if a conductive path is provided. Voltage represents the driving force that impels charge carriers to move. If all other factors are held constant, high voltages produce a faster flow of charge carriers, and therefore larger currents, than low voltages. But that’s an oversimplification in most real-life scenarios, where other factors are hardly ever constant!