From Newton’s law of motion we know that there is a reaction for every action. Production of current flow or generation of power at power plants both require huge work to be done. But as work is done there will be reaction of that work too. During electricity generation water power ( potential ), thermal power, mechanical power, are converted into electrical power. Since we cannot use electric power directly we need to convert it into another usable power too like heat, light, or mechanical power etc. When current flows through a wire some loss occurs and this loss is almost inevitable, the more the resistance of wire, the more the loss. This loss due to the electrical resistance of wire is mainly responsible for the heating effect of electric current.
As some power is converted into heat energy, this phenomenon can be described by Joules law, which states that H = i².r.t, where H is the generated heat in calories, i is the current that is flowing through the wire and it is measured in amperes, r is the resistance of the wire in ohm(Ω) an and t is the duration of current flowing in seconds. If we know the time of current flowing, resistance of wire, amount of current flow, we can easily find out the generated heat of the circuit. This heat can be utilized in various ways.

Applications

We saw that the more the electrical resistance of the wire the more the generated heat in the circuit but to know more accurately about the heating effect of current we should know it in the atomic level. As the flow of electric current is nothing but flow of electrons there will always be resistance from the fixed atoms of the wire. The fixed atoms of the wire resist the flow electrons and as a result there are collisions and as the kinetic energy converts into heat energy we see that the wire is getting hot

Now the generated heat can be viewed from many points of angles. Sometimes it is only seen as loss and is tried to be minimized. Various steps are taken to minimize heat dissipation from the conductor. But many positive application of this heating effect we can see in our daily life. Electric iron, the whole idea or working principle depends upon the heating effect of electric current. High resistant wire is used as the main coil in the electric iron when current flows through the coil, the coil gets heated and the iron works. But what about over heating of electric iron ? This problem can be overcome by using bimetallic conductors. Metal plates made of two different metals are used in the circuit. As expansion co-efficient of heat is different for two metals so due to heating effect one metal’s expansion is different from the other metal as a result the plate is bend and after reaching or certain temperature the contact of the circuit is broken and current flow through the coil is stopped and the electric iron too is not heated anymore.

Same mechanism is used in electric heater the only difference is that there is no bimetallic plate or circuit breaker involved.
Another application of heating effect of current is seen in electric bulbs. The wire which is used inside the bulb gets illuminated and emits light after reaching certain temperature. The metal used in bulb mainly made tungsten.
Finally and perhaps the most important application of heating effect of electric current is in electrical fuses, which are used in almost everywhere. From huge industries to domestic level, everywhere electric fuse is must. Fuse is made of such metals which has certain melting point. They are okay for normal current but when over current flows through the circuit the generated heat in the fuse wire is enough to melt the metal portion of the fuse wire and break the circuit. In this way the costly equipment are protected as huge current flow, can damage the equipments permanently.