Current Electricity-Applications: Heating Effect of Electric Current

Introduction:

Electricity is a form of energy. It is an everyday observation that when electricity is passed through a conductor, then it becomes hot and the temperature starts to rise. This phenomenon is also known as the heating effect of electric current. Also, the heating effect of electric current has a wide range of applications which we utilise in our day-to-day life like electric heaters.

Causes of heating:

The heating effect of electric current takes place due to the changes which take place at the microscopic level. When the current is passed through any conductor the electrons start drifting from the positive terminal of the cell to the negative terminal of the cell. Any physical object provides some resistance to the current passing through it. The electrons collide violently with the atoms, ions, and molecules present in the conductor. This collision increases the average amplitude of vibration of the ions, atoms, and molecules which in turn increases the average temperature of the conductor (kinetic theory of matter).

Heating effect by electric current:

Let us assume that the current I is passing through a conductor of resistance R. As per the definition the charge passing through the conductor after time t  is defined as:

q=I*t

The potential energy across the conductor is defined as

 qV=i2Rt

This decrease in the potential energy across the conductor will appear as heat energy which increases the temperature of the conductor. This formula is also known as Joule’s law of heating which is another name for the heating effect of electric current.

 According to the Joules law of heating:

 As per the heating effect of electric current, the amount of heat energy produced on the conductor is:

•  directly proportional to the square of the current passing through it.
•  directly proportional to the distance of the conductor.
•  directly proportional to the time for which the current is being passed.

The heating effect of electric current is an Irreversible process. 

Different formulas for calculating heat produced: 

Let H be the heat produced by the conductor in time t.

H=I2Rt

P=H/t

P=I2Rt/t

P=I2R

Hence as per the heating effect of electric current, the power consumed by the conductor is directly proportional to the square of the current passing through it and resistance.

Again in the above equation, we can replace IR with V (potential difference between the conductor). Hence the Power consumed is also given by:

P=I*V

The power consumed is independent of time. The heat energy evolved depends on the time taken.

Series and parallel connections:

1. If resistances are connected in series then the power developed across the resistance having a higher magnitude of resistance will experience a greater rise in temperature. This is because in this case the amount of current across the conductor is the same but the resistance differs so the heating effect of electric current is determined only by the resistance.

P=I2R

2. If the resistances are connected in parallel then the power developed across the resistance having lower the magnitude of resistance will experience a small rise in temperature. This is because in this case, the potential difference across the conductors remains constant but resistance differs.

P=V2/R

Hence as per the heating effect of electric current, conductors having larger resistance experience smaller power.

Applications of heating effect of electric current:

1. The safety device- fuse is purely based on the principle of the heating effect of electric current. When more current than the recommended value is passed through the fuse then it overheats which melts the fuse and hence breaks it. As a result, current can no longer pass through the fuse and hence the household appliances are saved.
2. Many household devices like the electric heaters are based on the principle of the heating effect of electric current.
3. Decrease in the brightness of a bulb after long usage: It is a common observation that the brightness of an electric lamp decreases with time. This is because on passing electricity, the metal present inside gets evaporated slowly. This makes the filament thinner and thinner which ultimately decreases the brightness of the filament. This is a phenomenon observed due to the heating effect of electric current.

Conclusion:

The heating effect of electric current is caused by the obstruction of electrons by the atoms and iron present in the conductor. The heating effect of electric current is also known as the joules law of heating. When current is passed through the conductor the electrons move from the negative terminal to the positive terminal with a very high drift speed. The Electrons collide with the atoms and ions present inside the conductors. This increases the amplitude of vibrations of the atoms which results in an increase in the kinetic energy of the atoms and hence the overall temperature of the conductor. The phenomenon of heating effect of electric current is utilised in many devices like electric bulbs, heaters,geysers, presses, toasters, etc. An electric fuse is also based on this principle. When more current is passed through the fuse than the recommended value then the fuse gets cut due to melting. Hence the household devices are saved.