Energy exists in various forms such as mechanical energy, heat energy, chemical energy, electrical energy, light energy and nuclear energy. According to the law of conservation of energy, energy can be transformed from one form to another. In our daily life we use many devices where the electrical energy is converted into heat energy, light energy, chemical energy or mechanical energy. When an electric current is passed through a metallic wire like filament of an electric heater, oven or geyser, the filament gets heated up and here electrical energy is converted into heat energy. This is known as 'heating effect of current'. It is a matter of common experience that a wire gets heated up when electric current flows through it. Why does this happen? A metallic conductor has a large number of free electrons in it. When a potential difference is applied across the ends of a metallic wire, the free electrons begin to drift from the low potential to the high potential region. These electrons collide with the positive ions (the atoms which have lost their electrons). In these collisions, energy of the electrons is transferred to the positive ions and they begin to vibrate more violently. As a result, heat is produced. Greater the number of electrons flowing per second, greater will be the rate of collisions and hence more heat is produced. 1. Mathematical Expression for Heat Produced
2. Application of the Heating Effect of Current
Mathematical Expression for Heat Produced
Potential difference is a measure of work done in moving a unit charge across a circuit. Current in a circuit is equal to the amount of charge flowing in one second. Therefore, the work done in moving 'Q' charges through a potential difference 'V' in a time 't' is given by Work done = potential difference x current x time
W = VIt
The same can be expressed differently using ohm's law.
According to ohm's law V = IR
Therefore work can be expressed as