temperature, heat, reversible change, irreversible change, thermometer, lab thermometer, clinical thermometer

1. Heat and temperature
( grade 7 notes)( grade 7 notes)
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2. Heat
• Heat is a form of energy which can cause hotness
to a body.
• Heat can only be transformed to other form of
energy.
• When a body possess or gains heat energy it• When a body possess or gains heat energy it
tends to become hot.
• Example:- Water become hot when kept on a gas
stove burner. Here gas stove is the source of heat
and water is gaining this heat energy.
• But if a body looses heat it become cold
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3. - On gaining the object becomes hot
- On loosing heat object becomes cold
- Heat gets transferred from hot object to cold
objects.
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4. How does heat energy gets transformed
into other form of energy
• Example1:- In thermal power
station heat energy is
transformed into electrical
energy.
• Example 2:- In nuclear power
plant, nuclear energy gets
transformed into heat energy,
• Example 4:- In electrical bulb,
the electrical energy gets
converted into heat energy of
the filament which is then
converted into light energy.
• Example 5:- during working of
heater or geyser electricaltransformed into heat energy,
and then heat energy into
electrical energy.
• Example 3:- On rubbing palm
against each other, palms
become hot. Here mechanical
energy is converted into heat
energy.
heater or geyser electrical
energy gets transformed into
heat energy.
• Example 6:- In steam engine,
heat energy is transformed
into mechanical energy.
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5. Temperature
• The degree of hotness of a
body is called its temperature.
• when a object is heated it
becomes hot along with this
object will also expand.
• Cooling of object results in
contraction.
• Effects of heat:-
1. Change of state of matter:-
solid ice converts to liquid
when kept at room
temperature. When it is
heated more it converts into
vapour. But cooling cancontraction. vapour. But cooling can
reverse this process hence it
is reversible process.
2. Bring chemical change in a
substance:- Food getting
cooked when heated. Milk
forms curd when it is warm.
These changes cannot be
reversed hence they are
chemical changes.
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6. Temperature
• Effects of heat:-
3. Heat effects the living organisms:- mangoes grow
only in summer because of appropriate heat
during summer.
- Bacteria gets killed on high temperature that is- Bacteria gets killed on high temperature that is
why milk is pasteurised on high temperature.
4. Burning of substances occur due to heat:- wood,
coal, petrol etc catch fire on burning and produce
large amount of heat. Hence are used as fuel for
domestic and industrial purpose.
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7. Thermometer
• The device use to measure the temperature of an
object is called thermometer.
• Thermometer use scale to give the reading of the
temperature.
• Celsius:- This scale is most commonly used. Its written
as °C. Example 30°C
• In Celsius scale the freezing point of water is taken as• In Celsius scale the freezing point of water is taken as
0°C and that of boiling point of water is 100°C.
• The stem of thermometer carry marks as horizontal
lines to read particular temperature these marks are
called Calibrations.
• There are different types of thermometer clinical,
industrial, digital etc.
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8. Laboratory and clinical thermometer
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9. Difference between clinical and
laboratory thermometer.
Clinical thermometer
• A clinical thermometer is
shorter than laboratory
thermometer.
• Clinical thermometer is
removed from body to read
the temperature.
Laboratory thermometer
• A laboratory thermometer is
much longer than clinical
thermometer.
• Laboratory thermometer is
read while its bulb is in close
contact with the object.the temperature.
• Capillary of clinical
thermometer have a kink just
above its bulb.
• The range of clinical
thermometer is 35°C to 42°C .
• Clinical thermometer is use to
measure body temperature of
humans and animals.
contact with the object.
• Laboratory thermometer has
straight capillary.
• The range of laboratory
thermometer is 0°C to 100°C.
• Laboratory thermometer is
use to measure temperature
of chemical reactions and
laboratory processes.
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10. Precautions to be taken while reading
laboratory thermometer.
• For taking the reading with clinical thermometer, the bulb
of the thermometer should be in proper contact of object
whose temperature is to be measured.
• For example:- for taking temperature of boiling water in
beaker the thermometer had to be immersed in water and
not touch side of beaker.not touch side of beaker.
• The reading of the temperature should be taken without
removing the thermometer from its position.
• The eye of the observer should be at the same vertical level
as that of the mercury in the capillary tube.
• The thermometer should not be use to measure the
temperature below its lowest marking or above its highest
markings.
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11. How to use clinical thermometer?
• The thermometer must be washed preferably with
antiseptic lotion like dettol or spirit or at least with
clean water and dried with a clean cloth.
• Thermometer should be given soft 2 to 3 jerk to bring
mercury in capillary below 37°C.
• Thermometer should not hit any object while giving
jerk, otherwise the bulb will break.
• Thermometer should not hit any object while giving
jerk, otherwise the bulb will break.
• Note the mercury reading in proper light.
• Mercury is poisonous metal so make sure it does not
break in mouth while taking temperature. Or measure
temperature underarms.
• If mercury spills by accident then it can be picked up by
kneaded wheat dough by rolling it over mercury.
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