Before we go to school or to attend any function, we ensure that our clothes are crisp and not crimped. And for this, we use an iron to straighten out those clothes. Why do we only use an iron? What’s the mechanism behind the working of an iron? And why is an iron always hot? Well, this iron is the most basic example of heating effects of electric current in our everyday life. There are many such other devices that work on the heating effects of electric current. Let us study them below.
What are the heating effects of the electric current?
When a current flows through a conductor, heat energy generates in the conductor. The heating effects of electric current depend on three factors:
- The resistance of the conductor. A higher resistance produces more heat.
- The time for which the current flows. The longer the time the amount of heat production is high.
- Higher the current the amount of heat generation is also large.
Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I2Rt. This equation is the Joule’s equation of electrical heating.
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- Electric Current and Circuit Diagrams
- Electric Potential and Potential Difference
- Ohm’s Law and Resistance
Joule’s law states the amount of heat production in a conductor is :
- Directly proportional to the square of electric current flowing through it.
- Is directly proportional to the resistance of the conductor.
- Directly proportional to the time for which electric current flows through the conductor.
Symbols of components
Kirchhoff’s First Law
The sum of electric currents entering a junction is equal to the sum of the currents leaving the junction. Kirchhoff’s First Law is a natural consequence of the conservation of electric charge. If the currents entering a junction are positive, and the currents leaving the junction negative, the sum of the currents is zero.
ΣI = 0
(ΣI = 0 ⇒ I1 + I2 = I3 + I4 + I5)
Kirchhoff’s Second Law
The sum of electric potential differences along any closed loop in a DC circuit is zero. Kirchhoff’s Second Law is a consequence of the conservation of energy. A change in the electric potential change equals the change in electric potential energy per unit charge. If the electric potential is negative in the direction of electric current and the
increase in potential is positive, the sum of the changes in electric potentials along any closed loop in a dc circuit is zero.
ΣV = 0
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Application of heating effects of current
Electric heater and water heater
When these appliances are in connection with the supply of electricity they become hot but wires remain cold. They consist nichrome which has high resistivity and hence high resistance. Heat produced is directly proportional to the resistance of material through which the current flows.
The filament of an electric bulb consists of tungsten with a high melting point. A filament is enclosed in a glass envelope which is filled with nitrogen and argon gas. Since the resistance of thin filament is very high, amount of heat production is large same as the electric current that flows through the filament. Due to a large amount of heat production, the filament bulb becomes white hot. Hence filament of bulb emits light and heat.
Wires consisting of some materials melt quickly and break when large electric current passes through them. These wires are used for making electric fuses. All electrical circuits in all buildings consist of electrical fuses. There is a maximum limit on the current which can safely flow through a circuit. If by accident the current exceeds this limit, the wires may overheat and cause a fire. If a proper fuse is there in the circuit, it will blow off and break the circuit.
A fuse is thus a safety device which prevents damages to electrical circuits and possible fires.When large electric current flow through a circuit and hence through fuse wire, a large amount of heat production occurs. Due to this large heat production, the fuse wire melts and the circuit breaks so that the current stops flowing through the circuit.This saves the electric circuit from burning. Electric fuses have ratings as 1A,2A,3A,5A,10A.
The element of the electric iron constitutes alloys having a high melting point. Electric heater and geyser work on the same mechanism.
Learn about Magnetic Effect of Electric Current here.
Solved Example For You
Q. What is the expression for the electrical power spent in the flow of current through a conductor in terms of resistance and potential difference?
a. V2/R b. V/R2
c. VR d. V2R
Sol: a. V2/R
If a certain amount of dissipation of power happens for a given time, then energy is dissipated. Measurement of energy (power×time) happens in units of Joules and by including time (t) in the power formulae, the energy dissipation of a component or circuit can be calculated. Energy dissipation = Pt
or VI*t as P=VI.
When the time factor is ignored, the relationship is as follows:
P = V2/R as I = V/R