Heating Effect of Current

 

When an electric current is passed through a high resistance wire, like nichrome wire, the resistance wire becames very hot and produces heat. This is called the heating effect of current. The heating effect of current is obtained by the transformation of electrical energy into heat energy. Just as mechanical energy used to overcome friction is converted into heat, in the same way, electrical energy is converted into heat energy when an electric current flows through a resistance wire.

Thus, the role 'resistance' in electrical circuits is similar to the role of 'friction' in mechanics. 

We will not derive a formula for calculating the heat produced when an electric current flows through a resistance wire.

Application of the heating effect of current:

The important application of the heating effect of electric current are given below: 

1. The heating effect of current is utilised in the working of electrical heating appliances such as  electric electric kettle, electric toaster, electric oven, room heating, water heater (geysers), etc. All these heating appliances contain coil of high resistance wire made of nicerome alloy. When these appliances are connected to power supply by insulated Coper wires then a large amount of heat is produced in the heating coils (because they have high resistance), but a negligible heat is produced in the connecting wires electric heater made of nicerome glows because it becames red-hot due to the heating element (or coil) of an electric heater made of nicerome glows because it becomes red- hot due to the large amount of heat produced on passing current (because of its high resistance), but the cord or connecting cable of the electric heater made of copper does not glow because negligible heat is produced in it by passing current (because of its  extremely low resistance). The temperature of the heating element (or heating coil ) of an electric heating device when it becomes red- hot and glows is about 900°C.

• The heating effect of electric current is utilised in electric bulb 💡 (electric lamps) for producing light:

When electric current passes through a very thin, high resistance tungsten filament of an electric bulb, the filament of an electric bulb produces enormous heat but almost negligible heat is produced in the connecting wires of copper. This is because of the fact that the fine tungsten filament has very high resistance whereas copper connecting wires have very low resistance.

• Tungsten metal is used for making the filament of electric bulb because it has a very high melting point (of 3380°C). Due to its very high melting point, the tungsten filament can be kept white-hot without melting away. The other properties of tungsten which make it suitable for making filament of electric bulb's are it's high flexibility and low rate of evaporation at high temperature. 

Please note that when the tungsten filament of an electric bulb becomes white-hot and glows to emits light, then its temperature is about to emits light, then its temperature is about 2500°C!

If air is present in an electric bulb, then the extremely hot tungsten filament would burn up quickly in the oxygen of air. So, the electric bulb is filled with a chemically unreactive gas like argon or nitrogen (or a mixture of both). The gases like argon and nitrogen do not with the hot tungsten filament and hence prolong the life of the filament of the electric bulb. It should be noted that most of the electric power consumed by the filament of an electric bulb appears as heat (due to which the bulb becomes hot), only a small amount of electric power is converted into light. So, filament types electric bulb are not power efficient. On the other hand, tube-light are much more power efficient because they have no filament.