Explanation/ Reason/ Laws/ Rules/ Devices/ Practical – Heater and Electric Press.
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.
Electric Boilers Electric Radiators
Electric Towel
Electric Heaters
Rails
Electric Air Electric Water
Curtains Heaters
Electric Fires
