2016 Jan

Physics of Joule Heating

January 29, 2016

Physics of Joule Heating

Electrical heating appliances like heaters and geysers are some of the luxuries offered by science. All of us use them in daily life and a day without these appliances is a nightmare in the cold countries where temperatures go down to below zero levels. Electricity can get a lot things done like washing clothes, running computer, heating water and so on. But how does electricity generate heat? Is it the same reason why a computer gets heated up? Is there any relation between the heating of a computer and electric heaters? To know the answers read further.

Electricity or current is generated when a pole of high potential is connected with that of low potential. As we know every object tries to reduce its potential energy. At high potential region electrons have large amount of potential energy and to reduce this they move to low potential regions. This motion is associated with a loss of potential energy. From the law of conservation of energy, this energy should be converted to another form (as energy can neither be destroyed nor created but can only be converted one form to other.). Most of the potential energy of the electrons is converted to kinetic energy just like it is in the case of an object falling under the influence of gravity. But unlike in the case of object falling under the influence of gravity, some of the potential energy is also converted to heat energy. This happens because, when electrons move from one point to other in a conductor like an iron wire, they constantly bombard the atoms of the conductor and cause them to vibrate. When an object is heated the atoms in it vibrate and hence the temperature of the object rises. Similarly in the case of bombardment of atoms by electrons, the resulting vibrations cause the increase in temperature.

Thus conduction of charge through a wire causes heating of it and this phenomenon is called as Joule heating, a term we also encountered during our H2 Physics tuition classes on Electromagnetic Induction. Joule heating depends on the amount of current passed through the wire (I), time for which current is passed (t) and the resistance of the conducting wire (R). In a computer, large amounts of current passes through the processor and RAM to sustain various functions of the computer. This large amounts of current heats up the conducting material and hence the computer gets heated up. Similarly in the case of a heater or a geyser current passing through a conductor of high resistance heats up the devices. Thus Joule heating is the connecting link between heating of a computer and working of a geyser.

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