Heating Effect of Electric Current
Electricity is the most widely used form of energy we cannot see electricity, but we can
see its effects. The Electricity can produce different types of effects. Basically the effect of
electricity is conversion of Electrical energy into other form of energy, such as Light, Heat etc.
When electric current flows in a circuit, it produces various effects such as
Heating Effect
Luminous Effect
Chemical Effect
Magnetic Effect
Out of the above four effects Heating effect and magnetic effect are predominant. The
heating effect of electricity is one of common and unique effect. In this unit we will learn about
the heating effect of electric current, use, advantage and disadvantage of heating effect.
Have you ever checked the body of electric motor or the body of Fan or Bulb after long run?
Have you noticed the temperature of any electrical device before and after long run or glow?
Do you find that electrical devices become warm after long run?
If yes, do you know why the electrical devices become warm after long run?
When a potential difference or Voltage is applied across the ends of a conductive metallic
wire, the free electrons begin forced to move. When the electrons moves the electrons collide
with the atoms. In these collisions, energy of the electrons is transferred to the atom and the
atoms begin to vibrate more violently.
As a result of this collusion the heat is produced. Greater the number of electrons flowing
per second, greater will be the rate of collisions and hence more heat is produced.
This effect of electricity is called the “Heating Effect” of electricity. The amount of heat produced
by electrical device in unit time depends on the
Resistance offered by the electrical device (circuit) and
Amount of current flowing through the electrical device (circuit) and
The time (duration) of electric current flow.
The great scientist James Prescott Joule made experiments on heating effect of electric
current, he enunciated various factors that affect the heat generated. He had given an
expression to calculate the amount of Heat produced by the electricity current.
Joule’s Law:
In studies James Prescott Joule found that the heat produced by a heating element is directly
proportional to the square of the electric current (I) passing through the conductor,
H α I2 (Current)
And directly proportional to the resistance (R) of the conductor,
H α R (Resistance)
time (t) for which current passes through the conductor.
H α t (Time)
Joule’s concluded that the quantity of heat developed in a current carrying conductor is equal to
the product of the square of the electric current, the resistance of the conductor and the time of
flow of current through the conductor. If I is the current in ampere (A), R the resistance of the
conductor in ohm (Ω), t the time in seconds (s) then the heat H produced in joule (J), is
H = I2Rt
Using Ohm's law R=I/V, the above equation can be changed into different forms.
H = VI t
This is well known as Joule’s Law.
If we pass a current through a high resistive load higher amount of heat energy can
produced by conversion of electric energy. This effect to electric current is used in many
electrical appliances.
Application of heating effect of electric current:
The heating effect of electric current is utilized in many electrical heating appliances such as
Electric Iron, Room Heater, Water Heater (Immersion Rod), Heater etc. All these appliances
contain high resistance coils. These high resistance heating coils are made up of nichrome, an
alloy of nickel, chromium, maganese and iron. The reasons for using nichrome as a heating coil
are
� High melting point
� High resistance
� The coil can remain in red-hot condition for a long time.
When the appliances are connected with Electric Supply then a large amount of heat is
produced in the heating coils because of high resistance of connected of nichrome wire. We will
learn about some common electrical appliance using the heating effect of electric current to
convert the electrical energy into heat energy.
Electric Iron:
The conversion of electrical energy into heat energy is used in “Electric Iron”. The electric iron is
one of the common electrical appliances we had already learned about the use of electric iron in
class VI,
Construction:
The simple electric iron uses an element made of Nichrome strip insulated by mica. When the
current flows through the nichrome stripped wire, a heat produces and this heat makes the
bottom
of
electric
iron
hotter.
This
heat
is
used
for
ironing
of
cloths.
Temperature controlled Electric Iron:
In this type of electric iron a temperature sensor called thermo couple is used to control the
higher range of heating of Iron. When the temperature reaches to the defined maximum limit the
thermo couple disconnects the electric supply from iron element and stops the iron from further
heating.
Heater
The conversion of electric energy into heat is achieved by a process called electric heating.
Electric heaters are used for this conversion process. Electric heating finds many applications
in industrial as well as in cooking processes. For example if we consider electric heaters, its
working is very simple. It consists of an electrical resistor in it.
The electric heater works on the principles of Joule’s law of heating. According to this principle,
when electric current is passed through the resistor, then the conversion of electric energy into
heat energy takes place.
Types of electric heaters
You may be familiar with the fact that electric heaters come in many different forms. Some types
of electric heaters are:
1. Radiator heaters or space heaters
2. Convection heaters
3. Fan heaters or forced convection heaters
4. Electric Storage heaters
5. Domestic electrical under floor heating
6. Heat pumps
7. Electrode heater
8. Immersion heater
Electric storage heaters
One such form is the electric storage heaters which are used to heat bricks with the help of
electric energy. The procedure followed here is that the bricks are heated and so heat gets
accumulated and it gets slowly released over the course of the day when it is required. The
advantage of using electric heaters is that energy can be made available at cheaper electricity
prices. The bricks are heated at overnight because the demand for electricity is low at overnight.
Radiative heaters or space heaters
The radiative heaters have a heating element which is possible of reaching a high temperature.
Similar to a light bulb, the radiative heater element is kept inside a glass envelope along with a
reflector. This reflector is used to direct the output energy far away from the body of the heater.
The heater element is capable of emitting infrared radiation. These infra red radiations are
capable of travelling through air and after hitting an absorbing surface these radiations are
converted into heat and gets partially reflected. This reflected heat serves the purpose of
heating the room and objects directly. In areas where spot heating is essential such as garages
and basements, the radiative heaters are used.
Advantages:
1. Silent operation of heaters
2. Easy to install
Convection heaters
Convection heaters work on the principle of convection. Generally we may know that hot air is
always less dense than the cool air. This makes the hot air to rise which in turn makes the cool
air to flow in to  the space left behind. This action produces a constant current of hot air. This
hot air leaves the heater with the help of vent holes provided in the appliance and this air is
responsible of heating the surrounding space. The heating effect will be more if the surrounding
space is a closed space.
Advantages:
1. Silent operation
2. Less risk associated with it when compared to radiative heaters
3. Chances of the heater getting burned are very low.
4. It affords much safety.
5. It is suitable for long heating period applications.
Fan heaters
Fan heaters are also called forced convection heaters. They are also a type of convection
heater. It consists of an electric fan which is used to speed up the air flow. Quick heating of the
surrounding can be done possibly with the help of fan heaters. This action of speeding up the
air flow helps to reduce the thermal resistance between the surrounding air and the heating
element and so heat can be transferred at a much faster rate.