Download File - electro science club

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?
Have 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.
1
Heating Effect of Electric Current
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, manganese and iron. The reasons
for using nichrome as a heating coil are
� High melting point
� High resistance
2
Heating Effect of Electric Current
� 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.
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.
3
Heating Effect of Electric Current
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.
Bread Toaster:
The bread toaster is very common appliance used in
kitchen. It also works on the heating effect of
electric current. A coil of nichrome wire is used to
convert the electrical energy into heat energy.
Electric Grill:
The electric grill is also work on
heating principle of electricity.
This advance appliance is making
its space in our kitchen.
4
Heating Effect of Electric Current
Electric Kettle:
The electric kettle is an electrical appliance uses electric heater to
warm up the water and prepare the tea. This is very handy
appliance and being used in home as well as offices too.
Water Geyser and Instant Water Geyser:
This appliance is used in bathroom to warm up the
water during winters. The Geyser comes in different
shapes and capacity.
Bucket Immersion Rod:
The immersion rod or heater is also the appliance used to
warm up the water during winter. It also works on
principle of heating effect of electric current
5
Heating Effect of Electric Current
Hair Dryer :
The hair dryer is a common electrical appliance works
on heating effect of electric current. In Hair Dryer a
heating Coil is arranged in front of small fan. When fan
rotates and throw air. The passing air get warmth of
heating coil and helps to dry the hair.
There are many other electrical appliances which uses the heating property of
electricity to work. All these appliances converts electrical energy into heat energy.
Which is used by us for different kind of works.
6