READ IT FOR DAV CLASS 7CH 5

1. DAV INSTITUTIONS
ODISHA ZONE- 1
SUBJECT- SCIENCE
CLASS –VII
TOPIC- HEAT
Prepared By:
Mr. Rama Ballabh Pradhan
Ms Sonali Kumari Ratha
DAV Pt. SR PUBLIC SCHOOL,BHANJANAGAR

2. Book Link: PDF format
• https://drive.google.com/file/d/1vimkZ9i2WoRXVjzXIiUTzH9lX-
h0YW3E/view?usp=sharing

3. LEARNING OBJECTIVES
Students will be able to know:-
Definition of the topic of HEAT & TEMPERATURE.
 Difference between “HEAT & TEMPERATURE”
 The effects of Heat.
 Difference between “Clinical thermometer’’ and “Laboratory
thermometer’’.
The basics of Heat transfer.
The basic approach in minimizing heating/cooling.

4. INTRODUCTION
What do you feel when you touch a hot cup of tea/milk?
Ans : You take your hand back because of Its hotness. You
could feel/sense, the heat which is coming out of that hot cup.
What happens when you are down with fever?
Ans: When you touch your body, you feel that your
body is quite hot than the normal body.
Can you hold an ice cube for long time?
Ans : No, in this case also we take our hands back because
the ice cube is too cold, it is freezing.

5. Hot and cold:-
In our daily life we come across a number of objects. Some of them
are hot and some of them are cold.
Eg:- in summer, we find cemented floor to be 'hot’.
where as in winter its 'cold’.
Some objects are hotter than others and some are cooler than others.
OBJECTS COOL/COLD HOT/WARM
Cold coffee
Boiling water
Ice-cream
Spoon dipped in hot milk

6. Heat as energy
Heat is a form of energy ,( heat energy), that is transferred from one
body to another ,due to the existence of temperature difference
between them.
“Iron is hot and heat is transfer to the shirt.”
Transfer of a heat energy always takes place from the body at a higher
temperature to that at a lower temperature.

7. HEAT AND TEMPERATURE
HEAT : Heat is a form of energy which can cause hotness to a body.
Heat is the energy of a body that is due to the motion of its
constituents particles ( molecules).
Eg:Water becomes hot when kept on a gas stove burner. Here gas stove
is the source of heat and water is gaining this heat energy.
TEMPERATURE :The degree of hotness of a body is called its
temperature.

8. EFFECTS OF HEAT
When a body is heated, various types of physical and chemical changes are
observed to takes place.
Chemical changes:
Chemical changes take place only when the reactants are heated up.
Eg: Burning of paper, wood, plastic, baking a cake.

9. Physical changes:
a) Change in temperature:
 When you heat something or supply it with heat, its temperature rises.
 When you cool something, its temperature falls.
Eg: Summer is hot and winter is cold

10. b) Change of state:
 Addition, or removal, of heat to, or from, a body, can bring about a
change in its state.
Eg: On putting a tray of water in a refrigerator, the water freezes to form
ice.
When water is heated over a flame, it starts boiling and gets converted
into steam.
Liquid form Solid form
Vapour form
Liquid form

11. c) Thermal expansion:
 Most of solids, liquids and gases, are known to expand when they are heated
and contract when they are cooled.
 Expansion is greatest in gaseous, less in liquid and the least in solids.

12. MEASUREMENT OF TEMPERATURE
Name a reliable source to measure temperature of an object, without
touching it?
It is measured by a device called THERMOMETER.

13. The THERMOMETER
 It consists of a narrow capillary tube of glass
that is closed at its upper end and has a bulb
at its lower.
 The bulb is filled with mercury.
 Inside the capillary tube we can see a small
shining thread of mercury.
 The mercury , present in the bulb of the
thermometer, expands when heated.
 The extent of its expansion, and, therefore,
the length of mercury thread in the capillary
tube, depends on the extent of heating of
the thermometer.

14. Clinical thermometer
The thermometer used by us or doctors to measure the body
temperature when we have fever is a clinical thermometer.
The scale used to measure the temperature is known as Celsius scale
denoted by ˚C or Fahrenheit denoted by ˚F.
It reads temperature from 35 ˚C to 42 ˚C or from 94 ˚F to 108 ˚F.
There is a kink near the bulb which prevents mercury level from falling
on its own.

15. Digital thermometer:
The normal human body temperature is
the average body temperature of a large
number of healthy persons. It is quite
close to 36.9 ˚C (or 98 ˚F).
A body temperature close to 40 ˚C ( or
104 ˚F) indicates a condition of ‘high
fever’.
Now a days Digital ( electronic)
thermometers are preferred over the
conventional mercury thermometers.
These thermometer are easy to read as
they give a ‘LCD display’ of the
temperature of the person. They are also
mercury free.

16. Reading thermometer:
The difference, in the temperature of the two
fixed reference points, is called the range of
the thermometer.
The two scales, that have been in common
use, are the Fahrenheit and the Celsius
scales.
Wash the thermometer with an antiseptic
solution. Hold it firmly and give it a few
jerks to bring the level of mercury below 35
˚C.
Then place the bulb of the thermometer
under your tongue.
After one minute take out the thermometer
and note the reading. This will be your body
temperature.

17. Comparison of Fahrenheit (˚F) and
Celsius (˚C) scale readings
The temperature ‘T’ in degree Celsius (˚C) is equal to the temperature
‘T’ in degree Fahrenheit (˚F) minus 32, times 5/9.
T (˚C) = [ T (˚F) - 32 ] X 5/9
T (˚F) = [ T (˚C) X 9/5 ] + 32
Normal room
temperature
23 ˚C 72 ˚F
Normal human body
temperature
36. 9 ˚C 98.4 ˚F
Water boils at 100 ˚C 212 ˚F
Water freezes at 0 ˚C 32 ˚F

18. Precautions to be observed while using a
clinical thermometer:
Wash the thermometer in clean water.
Jerk the thermometer to bring the mercury thread below 36 ˚C.
While reading the temperature, do not hold the thermometer by the
mercury bulb.
After use, wash the thermometer before storing.

19. LABORATORY THERMOMETER-
 Range of laboratory thermometer is
generally -10 ˚C to 110 ˚C.
Precautions:
The laboratory thermometer should
be kept upright and not tilted.
The bulb shouldn’t touch the surface
of the container.
The bulb should be surrounded by
the substance from all sides.

20. Difference between laboratory
thermometer and clinical thermometer:
Clinical thermometer Laboratory thermometer
It is used to measure the body temperature. It is used to measure the temperature in
laboratory.
It is graduated from 35 ˚C to 42 ˚C or 94 ˚F
to 108 ˚F.
It is graduated from -10 ˚C to 110 ˚C.
There is a kink near the bulb to prevent the
fall of mercury level.
No kink is present, so mercury level falls
on it own.
Temperature can be read after removing it
from the source.
Jerks need not be given, mercury level falls
automatically.

21. TRANSFER OF HEAT:
How does heat flow?
HOT
COLD
The heat always flows from the hot body to cold body until they are not
both in equilibrium.

22.  Transfer of heat takes place, with the hot object losing some of
its heat, and the cold object gaining the ‘heat’.
Eg: a) When a metal chair is left out in the sun, on a hot
summer day, it becomes too hot to sit on.
b) Touching a stove and being burned.
c) when a glass of hot water is left on a table, it becomes
lukewarm after sometime.
There are three different methods of transfer of heat. They are
known as:
i. Conduction
ii. Convection
iii. Radiation

23. Conduction:
Mode of transfer of heat in solids in which heat
moves from molecules to molecules with out
any movement of the molecules themselves.
The body through which heat transfer must be
in contact.
The molecules vibrate about their mean
positions as they receive energy and pass it to
the surrounding molecule.
Eg: a) when one end of a needle is put in a flame,
its other end also soon becomes very hot.
b) Ice cooling down your hand.

24. Activity : 1
Take an iron or aluminum rod or strip.
Fix a few wax pieces on at equal distances. Clamp the rod to a stand.
Heat the other end of the rod.
The wax pieces begin to melt and fall down from the heated end.
This shows that heat is transferred from the hotter end to the colder
end by conduction.
VIDEO
https://youtu.be/4tfTViP5Y5c

25. Conductors and insulators:
Conductors Insulators/bad conductor
Materials that allow heat to pass
through them easily.
Materials that do not allow heat to
pass through them easily.
Eg: Steel, iron, silver Eg: Rubber, wood, thermocol

26. Convection:
Mode of transfer of heat, in liquids and gases, in which molecules
themselves move to carry heat.
Heat transfer takes place with the actual motion of matter from one
place within the body to the other.
Transfer of heat by actual motion of matter.
The cyclic movements of molecules, in liquids and gases, as
convection currents.
Convection current in air leading to winds and storms.
Eg : Hot air rising, cooling and falling ( convection current)

27. Activity -2
Take some water in around bottom flask.
Keep it on a wire gauge kept above tripod stand. Put a
crystal of potassium permanganate in it. Heat it with a
burner.
The water at the bottom becomes hot and rises up and
cold water from the top moves down and the process
continues till all the water gets heated.
This shows that heat is transferred by convection.

28. Convection in air:
The air near the heat source gets heated and rise up. The air from the
sides move in to take its place.
In this way the air gets heated.
If you keep one hand above a flame and one hand on the side of the
flame, the hand at the top feels hot because the air above is heated by
convection.
The hand at the side does not feel as hot because there is no convection.

29. What is Wind ?
What is the cause of wind?
GLOBAL WIND PATTERNS:
Wind is the horizontal movement
of air from an area of high pressure
to lower pressure.
There is uneven heating of earth
that result in the global wind
pattern.
Wind is caused by difference in
temperature and difference in
pressure.

30. Difference in temperature and difference in pressure
Warm air rises Rising air creates low pressure. If air is
lifted up, that means there is less air
pushing down on earth.
Warming air make the molecules move
faster and spread out. This makes the
air less dense . Less dense air is light
and will rise.
Sinking air creates high pressure . If air is
sinking , then air is pushing down on the
surface of earth with a high amount of
pressure.
Cold air sinks.
Cooling air makes the molecules move
slower and group together. This makes
the air more dense. More dense air
sinks.

31. TYPES OF WINDS
LOCAL WIND
 Local winds are the winds that
blow over short distances
GLOBAL WINDS
 Global winds are the winds that
blow steadily from specific direction
over long distances

32. During the day the land gets heated
faster than the sea. So the air above
the land gets heated and becomes rises
up and cool air from the sea moves
towards the land. This is called sea
breeze.
During the night sea cools down
slowly than the land. So the hot air
above the sea rises up and cool air
from the land moves towards the sea .
This is land breeze.
SEA & LAND BREEZES:

33. COMPARISION
LAND BREEZE
Also known as off-shore wind.
Formed at night..
Comes from land.
More often experienced during
autumn and winter months.
Weaker breeze.
Dry winds
Not that influential to aircraft
operations.
Doesn’t significantly influence
temperature changes.
SEA BREEZE
Also termed as on-shore wind.
Formed at daytime.
Comes from water.
More often experienced during
spring and summer months.
Stronger breeze.
Have moisture.
Substantially beneficial for the
glider pilots.
May significantly lower air
temperature.

34. Radiation is the process by which heat is
transferred from one place to another without
the help of any medium.
Eg. The heat from the sun reaches the earth by
radiation.
 When we sit near a fire we feel warm due to
the heat radiated by the fire.
APPLICATION OF RADIATION
Dark coloured surface absorb more heat than
light coloured surfaces and hence the bottom
of cooking utensils are coloured with black.
Dark coloured surface radiate more heat than
light coloured surface.
RADIATION:

35. Take two tin cans of same size. Paint the outer surface of one black and the
other white. Pour equal amounts of hot water of the same temperature. Leave
them in a room or shade for 10minutes. Measure the temperature of water in
both the cans . The water in the black can is warmer than the water in the white
can as well as the water in the black can is cooler than the white can.
We wear light coloured clothes in summer because it reflects most of the heat
and keeps us cool.
We wear woolen clothes in winter because wool is a poor conductor of heat and
the air between the wool fibers prevents loss of heat from our body. So we feel
warm.
ACTIVITY

36. Mind map
Heat
HEAT TEMPERATURE
EFFECTS OF HEAT
PHYSICAL
CHANGE
CHEMICAL
CHANGE
THERMOMETER
CHANGE OF STATE
THERMAL EXAPAN-SION
CHANGE IN TEMPERA-TURE
TRANSFER OF
HEAT
CLINICAL
THERMOM
-ETER
LABORATO
-RY
THERMOM
ETER WIND PATTERN
CONVECTION
CONDUCTION
RADIATION
LAND BREEZES SEA BREEZES

37. LEARNING OUTCOMES:
Students learnt about :
Acquire idea about heat and temperature.
Know the difference between heat and temperature.
Get idea of the effects of heat’.
Easily identify and know the use of clinical and laboratory
thermometer.
Know about convection, conduction and radiation.
Heat transfer from heating end to cooling end.

38. SAMPLE QUESTION
https://drive.google.com/file/d/1Cr4iY3F3oElcg
oZmuKWmCIqQrrQ96Fjv/view?usp=sharing

39. THANK YOU