transfer of heat genral science ppt

1. SUBJECT
Methods of teaching general science
CHAPTER NO 1:
Transfer of heat and concept of conduction,
convection and a radiation.

2. TRANSFER OF HEAT
 We know that when a hot body is brought in
thermal contact with a cold body, heat energy will
fellow from hot body to cold body. The fellow or
transfer of will continue till both side are at same
temperature thermal equilibrium is achieved. This is
illustrated by following examples.
 Take a cup of hot tea and leave the cup on the table
in the room for the some time. We will observe that
the from hot tea flows to the environment of room
because it is low temperature and acquires same
temperature after some time.

3. TRANSFER OF HEAT
 Leave a bowl of cold water in the room for few
mints we will observed that ice cream is melted. In
the present case, heat energy flows from
environment to ice cream because the temperature
of room is high as compared to ice cream.
 The transfer of heat plays an important role in our
daily life and industries. There are three
mechanisms by which the heat transfer take place.
They are as under.

4. TRANSFER OF HEAT
 Conduction
 Convection
 Radiation
The above process may involve in transfer of heat
from region of high temperature to region of low
temperature depending upon the situation.

5. CONDUCTION OF HEAT
 In this mode, heat is transfer from its high
temperature region to low temperature region by
the vibration of atoms or molecules about their
mean positions without any actual movement f
atoms or molecules from one place to another. If
the given material is metal, free electron present in
it do contribute in transfer of heat from hot region to
cold region. Electrons carry energy and move with
high velocity from hot region to cold region of metal.
 The mode of heat transfer can be understood by
the by the following simple experiment.

6. CONDUCTION OF HEAT
 Hold one end of a metal rod such as iron or copper in
your hand and place the other end in a fair. Was We will
observe that the end of metal or rod in your hand also
slowly becoming hot. We will find difficult to hold the rod
after few minutes although it was not in direct flame. The
atoms of rod retain their positions and don't move from
the hot end to cold end. How does the transfer of heat
takes place?
 The metal rod may be regarded as consisting of layers of
atoms which are closely packed. The atoms of layer
adjacent to flame start vibrating about their mean position
with larger amplitude after absorbing heat energy from
the flame.

7. CONDUCTION OF HEAT
 In a solid, atom are very close to one another
therefore the atoms is of first layer compel the
atoms of second layer of atoms to vibrate with large
amplitude. As the first layer of atoms continuously
absorbing heat energy from flame and vibration of
atoms are being transferred to next layer of atoms.
 Supplely, the conduction is the mode of transfer of
heat in the solid material from its high temperature
region to low by vibration of atoms or molecules
about their mean positions without any actual
movement of atoms of molecules from one place to
another.

8. QUESTION FOR DISCUSSION
Does Styrofoam is a conductor?

9. DOES STYROFOAM IS A CONDUCTOR?
 Styrofoam is a poor conductor of heat. Food
container made of Styrofoam are capable of
retaining foods like burger, tea etc. hot as well as
ice cream cold for longer time.

10. CONVECTION
 Convection is another mode of heat transfer in this
mode, heat is transferred by actual movement of
hot molecules from hot region to cold region . We
know molecules can move from one to another
place only in fluid, liquid and gas.
 Thus convection take place in liquid and gas not in
solid. Convection is more efficient method as
compared with conduction for transfer of heat.
There are two types of convection are below;
 Natural convection
 Forced convection

11. TYPES OF CONVECTION
 Natural convection:
In natural convection a fluid flows due to difference in the
density created by due to heating of fluid. The boiling of
water in a container on heating is the good example of
convention currents in the liquid.
On heating, the hot water rises due to its less density and
replaced by high density cold water. The movement of
water in natural convection current causes the water to
boil.
When a gas or eclectic heater is switched on; room is
heated due to convection current of air which are set up
due to heating air surrounding the heater. The
ventilation of building also works convection in fluids.

12. TYPES OF CONVECTION
 Forced convection:
In forced convection a blower, fan or suction device
is used to direct the heated in given direction and
destination. The examples of forced convection are
mention below:
The engine of vehicle such as car, bus or truck etc, is
cooled by convection current in water pipes.
In a simple domestic hot water system. When water
is heated by a boiler, convection current are set up
in water which forced its movement in pipes. A
storage tank is used for continuous supply of hot
water in the house.

13. RADIATION
 Sun is the main source of light and heat on our
planet Earth. Radiation is the mode of heat transfer
from one place to another place in the form of
electromagnetic waves. There is no material
medium in between sun and earth. The region
between then is empty or vacuum exists between
these two heavenly object. That is why these waves
can travel in vacuum.