Heating Effect of Electric Current: Definition, Joule’s Law, Examples

We see the applications of the heating effect of electric current in our daily lives. We use room heaters in winters to keep the temperature of our room greater than the outside temperature. We use electric geysers in the winter season. When an electric current passes through a conducting wire, the wire becomes hot because of the generation of heat in the wire. This process is defined as the heating effect of electric current.

The heating effect of electric current can be seen in various gadgets like electric bulbs, fuse, geysers, iron, etc. Let us learn more about the heating effect of electric current.

What is the Heating Effect of Electric Current?

When an electric current flows through a high resistance conducting wire, heat is produced in the conducting wire. This is called the heating effect of electric current. The heat is generated in the wire because when the electrons flow in it, they experience hindrance to their movement by other electrons and by the lattice atoms. This causes the electrons to lose some of their energy in the form of heat.

The loss of energy is compensated by the source to maintain a uniform current in the wire. So essentially, some of the energy provided by the source of electricity gets converted in the form of heat energy. The larger the resistance offered by the conductor to the flow of current, the large will be the generation of heat in it.

Joule’s Law of Heating

Joule’s law of heating describes the factors on which the heat generated in a conductor depends when an electric current is passed through it. Let us assume that a current \(\left( I \right)\) flows through a resistor of resistance \(\left( R \right)\) for time \(\left( t \right).\) Let \(\left( Q \right)\) be the electric charge that flows across the resistor, then the work done required in moving this charge is given by

\(W = VQ\;\;\;\;\;\;\; \ldots \left( 1 \right)\)

Where \(V\) is the potential difference across the resistor.

The power of the source, \(P = \frac{W}{t}\)

By substituting equation \(\left( 1 \right),\) we will get \(P = \frac{{VQ}}{t} = V\left( {\frac{Q}{t}} \right)\;\;\;\; \ldots \left( 2 \right)\)

We know that the electric charge is given by

\(Q = It\)

So, the power of the source will be given by \(P = VI\;\;\;\; \ldots \left( 3 \right)\)

From Ohm’s law, the potential difference is the product of current and resistance.

\(V = IR\)

By substituting the value of \(V\) in equation \(\left( 3 \right),\) we get

\(P = {I^2}R\;\;\;\;\; \ldots \left( 4 \right)\)

Now, the amount of heat energy dissipated in the resistor will be given by \(H = Pt = {I^2}Rt\)

This is known as Joule’s law of heating. According to Joules’s law of heating, the heat produced or dissipated in a resistor is \(\left( {\rm{i}} \right)\) directly proportional to the square of the current flowing through the given resistor, \(\left( {\rm{ii}} \right)\) directly proportional to the resistance for a given current, and \(\left( {\rm{iii}} \right)\) directly proportional to the time for which the current flows through the resistance.

From Joule’s law of heating, we can conclude the following statements:
1. If the amount of current flowing through a resistor is doubled, then the heat produced will become four times.
2. If the resistance of the conductor is doubled, then the heat produced will also get doubled. Similarly, the heat produced in the conductor reduces to half when the resistance of the conductor becomes half.
3. If the time for which the current is passing through the conductor is doubled, then the heat produced is doubled.

Applications of Heating Effect of Electric Current

All devices do not generate heat on passing electricity through them. Devices that use high resistance wire as a heating element can only produce a considerable amount of heat on passing electricity through them. Nowadays, we are using many electrical devices that work on the heating effect of electric current. Some of the electrical devices that work on the heating effect of electric current are as follows:

1. Electric Bulb: An electric bulb consists of a filament that is made of tungsten. Tungsten wire has a high resistance, and it can withstand a large amount of heat because the melting point of tungsten is \({\rm{3380}}{{\rm{\;}}^{\rm{o}}}{\rm{C}}{\rm{.}}\) When electricity is passed through the filament of the bulb, it becomes very hot and glows because its temperature rises up to \({\rm{2500}}{{\rm{\;}}^{\rm{o}}}{\rm{C}}{\rm{.}}\) If we place our hand below the bulb, we can easily sense the heat produced by its filament without touching it. To increase the life of tungsten filament and to avoid the corrosion of filament, an electric bulb is filled with a mixture of argon and nitrogen.

2. Electric Fuse: An electric fuse works as a safety device. It protects the appliances connected to the household circuit from getting damaged due to overloading or short-circuiting. It works on the heating effect of electric current. It consists of a thin wire usually made of an alloy of lead and tin. It has a low resistance. It is connected in series with the circuit. When excessive current passes through a fuse wire, it heats up and melts down. This breaks the circuit and protects the appliances connected to the circuit from getting damaged.

3. Electric Heater: An electric heater consists of a heating element made of nichrome. It has a high resistance. When an electric current flows through the heating element of the electric heater, it generates heat energy.

4. Electric Iron: A coil of nichrome wire is used in an electric iron. When electricity passes through this coil, it becomes red-hot and produces heat which is then transferred to the plate attached at the base of the electric iron.

5. Electric Geyser: The electric geyser converts electrical energy into heat energy when an electric current is passed through its heating element, which is attached to the water tank of the geyser. An electric geyser uses a thermostat that automatically cuts the power supply once the water in its tank is heated to a required temperature level.

Solved Examples on Heating Effect of Electric Current

1. Calculate the heat given out by a filament of the bulb in \({\rm{20\;s,}}\) when its resistance is \(4\;{\bf{\Omega }}\) and the potential difference across its ends is \({\rm{12\;V}}{\rm{.}}\)
Sol: Given, the time for which the bulb glows, \(t = 20\;{\rm{s}}.\)
The resistance of the bulb’s filament, \(R = 4\;{\rm{\Omega }}.\)
The potential difference across its ends, \(V = 12\;{\rm{V}}.\)
The heat given out by the filament can be calculated by the following equation:
\(H = \left( {\frac{{{V^2}}}{R}} \right)t\)
By substituting values, we get
\(H = \left( {\frac{{{{12}^2}}}{4}} \right) \times 20\) \( \Rightarrow H = \frac{{144}}{4} \times 20 = 720{\rm{\;J}}\)

2. An electric heater having resistance \(5\,\;\Omega \) is connected to a source of electricity. If it produces \({\rm{200\;J}}\) of heat in one second, find the potential difference across the electric heater.
Sol: Given, the resistance of the electric heater, \(R = 5\;\Omega \)
The heat produced by the heater, \(H = 200\;{\rm{J}}\)
The time for which the heat is produced, \(t = 1\;{\rm{s}}\)
To calculate the potential difference across the heater, we need to know the amount of current passing through it.
The current flowing through the heater can be calculated by using the following formula:
\(H = {I^2}Rt\)
\( \Rightarrow I = \sqrt {\frac{H}{{Rt}}} \)
\( \Rightarrow I = \sqrt {\frac{{200}}{{5 \times 1}}}  = \sqrt {40}  = 6.324\;{\rm{A}}\)
Now, the potential difference across the electric heater can be calculated using Ohm’s law.
\(V = IR\) \( \Rightarrow V = 6.324 \times 5 = 31.62\;{\rm{V}}\)

Summary

From this article, we can conclude that when electricity is passed through a conductor, it becomes hot because of the heating effect of the electric current. The heat produced in a conductor depends on the resistance of the conductor, current flowing through the conductor and the time for which the current flows through the conductor. This effect of electric current is used in many household gadgets. The applications of the heating effect of electric current can be seen in several electronic gadgets such as electric water heaters, electric room heaters, electric fuses electric bulbs, etc.

FAQs on Heating Effect of Electric Current

1. Why is heat produced in a conductor on passing an electric current through it?
Ans: When a potential difference is applied across the ends of an electric conductor, the electrons start moving in the conductor, causing a current to flow in it. These electrons experience many resistive forces in their path, so to maintain the uniform flow of the current in the conductor, the source of electricity loses some energy in the form of heat energy.

2. What is the working principle of an electric fuse?
Ans: An electric fuse works on the heating effect of electric current. It heats up and melts down to break an electric circuit when an excess of current flows through the circuit.

3. What do you mean by the heating effect of electric current?
Ans: The generation of heat energy in a conductor whenever an electric current passes through it is called the heating effect of electric current.

4. What are the disadvantages of the heating effect of electric current?
Ans: Energy dissipation in the form of heat in electric conductors reduces the efficiency of the source of electricity. Sometimes, the excessive heat produced in a conductor on passing electricity through it results in the damage of electrical devices and causes short-circuiting.

5. What are the advantages of the heating effect of electric current?
Ans: Many electronic gadgets like electric water heaters, electric room heaters, electric fuses and electric bulbs work on the heating effect of electric current.

NCERT Solutions for Current and its Effects

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