Heating effect of current : Consider a purely resistive circuit, that is a circuit which consists of only some resistors connected to a battery. The energy of the battery gets dissipated entirely in the form of heat produced in the resistors. The phenomenon of production of heat in a resistor by the flow of an electric current through it is called heating effect of current or Joule heating.
Cause of heating effect of current : When a potential difference is applied across the ends of a conductor, it s electrons get accelerated from negative terminal to positive terminal. During the course of their motion, these electrons collide frequently against one another and against the atoms of the conductor. At each collision, a part of kinetic energy of the electron gets converted into heat and this increases the temperature of the conductor.
Practical applications of heating effect of electric current : Some of the useful applications of heating effect of current are as follows :
1. Household heating appliances : Most of the electrical appliances used in daily life are based on heating effect of current such as room heater, electric toaster, electric iron, electric oven, electric kettle, geyser. The heating element used in these appliances should have high melting point and high resistivity.
2. Incandescent electric bulb : It is an important application of Joule heating effect. It consists of a filament of a fine metallic wire enclosed in a glass bulb filled with chemically inactive gases like nitrogen and argon. The filament material should have high resistivity and high melting point. Therefore, tungsten (melting point 3380oC) is used for bulb filament. When a current is passed through the filament, it gets heated to a high temperature and emits light.
3. Electric fuse : It is a safety device used to protect electrical appliances from strong currents. A fuse wire must have high resistivity and low melting point. It is usually made from an alloy of tin and lead. It is put in series with the live wire of the circuit. When the current exceeds the safety limit, the fuse wire melts and breaks the circuit. The electric installations are thus saved from getting damaged.
The fuses used for domestic purposes are rated as 1A, 2 A, 3A, 5A, 10A. For an electric iron which consumes 1kW electric power when operated at 220 V, a current of (1000/220) A, that is, 4.54 A will flow in the circuit. In this case, a 5 A fuse must be used. |
