Question

Question 34
What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.

Answer 1

Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. The amount of heat released is proportional to the square of the current such that
$H\propto I^2.R.t$
In some cases, Joule heating is pertinent to an electrical device's design, while in others, it is an unwanted effect.
A couple of applications that do rely on Joule heating include hot plates (directly) and micro valves for fluid control (indirectly, through thermal expansion).

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, 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 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.