Practical Applications of Joule's Heating

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This heating is inevitable in any electrical circuit. Since the energy lost by the flowing charges ends up as disorderly thermal motion, the phrase 'ohmic dissipation' is also used to describe it. Often, this is an undesirable effect. For example, in electric circuits, the heat produced in a small region, can increase the temperature of the components so much that their properties change. Also to decrease ohmic losses, power transmission over long distances is effected at high voltage so that the current is reduced.

In many cases however, Joule heating is very useful. One common application is the fuse used in electric circuits. It is a short piece of metal, inserted in a circuit, which melts when excessive current flows through it and thus breaks the circuit. It thus protects appliances. The material of a fuse generally has a low melting point and high conductivity.

Familiar domestic applications are the electric iron, bread toaster, even electric kettle, heater, etc.

Electric heating is also used in producing light, as in an incandescent bulb. Here, the filament is made of a resistor that retains as much of the heat generated as possible. Then it can get very hot and emit light. It must not melt at the high temperature. Usually, tungsten is used for the bulb filament, as it has a high melting point (6116^oF) and is a strong metal. A small amount of the power used by the filament appears as radiated light, but most of it appears as heat.