Definition
Heat is definitely the change in the temperature of a body.
Heat makes us feel a sensation of hotness. It is a form of energy produced from
different sources. Heat is usually transferred from one region to another until
the heat content between the two bodies are uniform.
Heat makes us feel a sensation of hotness. It is a form of energy produced from
different sources. Heat is usually transferred from one region to another until
the heat content between the two bodies are uniform.
Production of heat
Heat is being produced by the sun, called solar heat. Heat
is equally produced by friction; Example heat produced when we eventually rub
our hands or palms together, vigorously for 30 minutes. The heat produced
between the tyres of vehicles and the ground when break is applied is due to
friction. Heat could also be produced during chemical reactions, as one
observes when tetraoxosulphate (vi) acid is introduced into a test tube of
water.
is equally produced by friction; Example heat produced when we eventually rub
our hands or palms together, vigorously for 30 minutes. The heat produced
between the tyres of vehicles and the ground when break is applied is due to
friction. Heat could also be produced during chemical reactions, as one
observes when tetraoxosulphate (vi) acid is introduced into a test tube of
water.
Uses of heat
Heat serves man in various ways; like our food, drying our
clothes and warming our homes. In industries, heat is used for separating metals
from their ores. The heat from the burning fuels in engines, provide vehicles
and airplanes with the ability to move. Again, heat from the burning of coal
provides train with the ability to move.
clothes and warming our homes. In industries, heat is used for separating metals
from their ores. The heat from the burning fuels in engines, provide vehicles
and airplanes with the ability to move. Again, heat from the burning of coal
provides train with the ability to move.
Most importantly, heat from fire wood, charcoal assist domestically
in cooking and roasting, in some cases drying and frying.
in cooking and roasting, in some cases drying and frying.
Heat serves as a source of energy for driving and diving. The
infinite application and uses of energy can’t be over emphasis.
infinite application and uses of energy can’t be over emphasis.
Since heat can do all of the above, consequently, we can
define heat as a form of energy called thermal energy which determines the
direction of flow and the temperature of the body.
define heat as a form of energy called thermal energy which determines the
direction of flow and the temperature of the body.
Concept of
Temperature
Temperature
Temperature is the measure of the average kinetic energy of
a body, according to kinetic theory. When a beaker of water Is placed over a Bunsen
burner for a while, the water gets hotter. The heat from the burner has
increased the temperature of water. Conversely, when we keep a cup of water
inside a refrigerator, the temperature seemingly decreases, this is due to the
fact that the heat is drawn from the water to the refrigerator, and hence the
water becomes cooler. Temperature can
also be broadly define as the degree of hotness or coldness of a body.
a body, according to kinetic theory. When a beaker of water Is placed over a Bunsen
burner for a while, the water gets hotter. The heat from the burner has
increased the temperature of water. Conversely, when we keep a cup of water
inside a refrigerator, the temperature seemingly decreases, this is due to the
fact that the heat is drawn from the water to the refrigerator, and hence the
water becomes cooler. Temperature can
also be broadly define as the degree of hotness or coldness of a body.
Effect of heat on
matter
matter
It has been observed and recorded that whenever heat is
applied to a body, various changes take place. These changes include the following:
applied to a body, various changes take place. These changes include the following:
(i)
Chemical changes
Chemical changes
(ii)
Change in physical property
Change in physical property
(iii)
Change in temperature of the body
Change in temperature of the body
(iv)
Change of state of the body
Change of state of the body
(v)
Expansion of the body
Expansion of the body
(vi)
Change in pressure of the body
Change in pressure of the body
(vii)
Thermionic emission occurs ( means emission of electron from metallic surface)
Thermionic emission occurs ( means emission of electron from metallic surface)
If one or more than one of the above changes takes place after heat is
applied to a body, the body may change in size or assume a different form (e.g one
can change from solid to liquid, and liquid to vapour)
applied to a body, the body may change in size or assume a different form (e.g one
can change from solid to liquid, and liquid to vapour)
How
temperature is been measured
temperature is been measured
Temperature of a body is measured with an instrument called thermometer.
There are various types of instruments; each makes use of different substances,
called thermometric substances, which changes with change in temperature.
There are various types of instruments; each makes use of different substances,
called thermometric substances, which changes with change in temperature.
Common thermometers are mercury in glass thermometers, liquid in glass
thermometer, gas thermometers, resistance thermometers..
thermometer, gas thermometers, resistance thermometers..
The kinetic theory of matter
The kinetic theory of matter was postulated to back up the movement of
tiny particles of matter, this postulate assumes that atom, molecules and ions
are constantly in a state of rapid and random motion and as such possess
kinetic energy.
tiny particles of matter, this postulate assumes that atom, molecules and ions
are constantly in a state of rapid and random motion and as such possess
kinetic energy.
The postulates are as follows
1.
All matter are made up of tiny particles called
atoms, molecules and ions
All matter are made up of tiny particles called
atoms, molecules and ions
2.
These particles are constantly in a state of
continual motion
These particles are constantly in a state of
continual motion
3.
As a result of this constant motion, they all
tend to possess kinetic energy
As a result of this constant motion, they all
tend to possess kinetic energy
4.
All the particles exert attractive forces on
each other
All the particles exert attractive forces on
each other
5.
The nearer the particles are to each other, the
greater the attractive force.
The nearer the particles are to each other, the
greater the attractive force.
6.
The temperature of the particles is directly proportional
to their increased volumes
The temperature of the particles is directly proportional
to their increased volumes
Using kinetic energy to explain the temperature of a body
According to kinetic theory of matter, we observed
experimentally that every object tends to possess kinetic energy when
undergoing or in a state of motion. If heat is proportionally applied to these
moving particles, consequently their individual velocities increases and this of
course result in the increase in the sequent average kinetic energy (1/2MV2).
This no doubts lead to increase in temperature
experimentally that every object tends to possess kinetic energy when
undergoing or in a state of motion. If heat is proportionally applied to these
moving particles, consequently their individual velocities increases and this of
course result in the increase in the sequent average kinetic energy (1/2MV2).
This no doubts lead to increase in temperature
Additionally, if the heat is reduced or completely withdrawn
from the body, the velocities of the molecules or particles also reduces or impedes
geometrically, which will result in the diminution of the temperature. This fact
actually reveals that if the temperature of the molecules increases, then the
kinetic energy of the molecules also increases and vice versa.
from the body, the velocities of the molecules or particles also reduces or impedes
geometrically, which will result in the diminution of the temperature. This fact
actually reveals that if the temperature of the molecules increases, then the
kinetic energy of the molecules also increases and vice versa.
Thermal expansivity of solids and liquid
Thermal expansion of
solids
solids
Solid expands when heated and contract when cooled. The rate
of expansion and contraction differs for different types of solid. It depends
on the material that the solid is made of .For instance, the rate of expansion
of brass is much more than that of iron and brass equally expands more than
invar.
of expansion and contraction differs for different types of solid. It depends
on the material that the solid is made of .For instance, the rate of expansion
of brass is much more than that of iron and brass equally expands more than
invar.
Ball and ring
Experiment
Experiment
When the metal ball is heated for some minutes and made to
pass through the ring, it is found that, it would no longer pass through the
same ring it passed before heating. This is due to the expansion of the ball. If
the ball is left to cool, and it is once more passed through the ring, it
passes easily, showing that it has contracted back to its original size.
pass through the ring, it is found that, it would no longer pass through the
same ring it passed before heating. This is due to the expansion of the ball. If
the ball is left to cool, and it is once more passed through the ring, it
passes easily, showing that it has contracted back to its original size.
The effects of expansion in everyday life
Some common and well
known effects of expansion are observed in
known effects of expansion are observed in
Rail way lines and metal bridges
Tall and high rise buildings
Wires and metal cup surfaces especially Telephone wires,
PHCN,TV Etc.
PHCN,TV Etc.
Railway lines and
metal bridges: Gaps are left in between sections of rail on a rail way
line; this is to allow for expansion and contraction when the temperature
increases or decreases respectively. In metal bridges, one end of the bridge is
allowed for expansion or to rest on rollers, while one is fixed, this is to
allow for expansion. During a very hot weather, as expansion occurs, the
end on roller continues to roll. If the
two ends are fixed, then no allowance is made for expansion, hence the bridge
could bend or crack.
metal bridges: Gaps are left in between sections of rail on a rail way
line; this is to allow for expansion and contraction when the temperature
increases or decreases respectively. In metal bridges, one end of the bridge is
allowed for expansion or to rest on rollers, while one is fixed, this is to
allow for expansion. During a very hot weather, as expansion occurs, the
end on roller continues to roll. If the
two ends are fixed, then no allowance is made for expansion, hence the bridge
could bend or crack.
Buildings:
Expansion or contraction of galvanized iron sheets used in roofing of some
buildings, generates cracking noise, which is heard when one is under the roof
of such building
Expansion or contraction of galvanized iron sheets used in roofing of some
buildings, generates cracking noise, which is heard when one is under the roof
of such building
In telegraph wires
: During hot weather the metals used in constructing these wires,
expand and sag, while during cold weather, they contract. To give room for
these effects, the wires are originally given some allowance to allow for the
expansion as well as contraction.
: During hot weather the metals used in constructing these wires,
expand and sag, while during cold weather, they contract. To give room for
these effects, the wires are originally given some allowance to allow for the
expansion as well as contraction.
Application of
Expansion
Expansion
Expansion is applied in removing a tight stopper of a glass
bottle without cracking either the bottle or the stopper. This is done by
standing the bottle in boiling waters, making sure the stopper is not in the
water. As the bottle in boiling water expands, the stopper whose size does not
alter, comes out loose.
bottle without cracking either the bottle or the stopper. This is done by
standing the bottle in boiling waters, making sure the stopper is not in the
water. As the bottle in boiling water expands, the stopper whose size does not
alter, comes out loose.
One of the most important applications of expansion is seen
in a bimetallic strip, which is used in the construction of a thermostat, a
device for maintaining a steady temperature. The thermostat is used in electric
laundry irons, in refrigerators and hot water storage.
in a bimetallic strip, which is used in the construction of a thermostat, a
device for maintaining a steady temperature. The thermostat is used in electric
laundry irons, in refrigerators and hot water storage.
The bimetallic strip thermometer: This is made up of a
coiled bimetallic spiral strip. The inside metal is usually made of invar or
steel that hardly expands, while the outside is made up of brass. One end of
the spiral strip is fixed and the other end is attached to the spindle pointer.
coiled bimetallic spiral strip. The inside metal is usually made of invar or
steel that hardly expands, while the outside is made up of brass. One end of
the spiral strip is fixed and the other end is attached to the spindle pointer.
Working of a
thermostat in electric laundry iron:
thermostat in electric laundry iron:
A bimetallic strip can be used to control the temperature of
an electric laundry iron. When the switch is set to any desired temperature
mark, then the current is on and the temperature of the iron increases. When
the a desired temperature is attained by the iron, the bimetallic strip
(thermostat) is now curved, and seperates from the contact point C , thereby
switching off the current, as the iron cools, the strip straightens up again
and remakes contact, thus switching on the electric current once more. This
makes and break device regulates and seemingly controls the internal and
external temperature of the electric iron.
an electric laundry iron. When the switch is set to any desired temperature
mark, then the current is on and the temperature of the iron increases. When
the a desired temperature is attained by the iron, the bimetallic strip
(thermostat) is now curved, and seperates from the contact point C , thereby
switching off the current, as the iron cools, the strip straightens up again
and remakes contact, thus switching on the electric current once more. This
makes and break device regulates and seemingly controls the internal and
external temperature of the electric iron.
