SUBTOPIC 9.2 HEAT FLOW AND THERMAL EQUILIBRIUM

CHAPTER 9
HEAT

PREPARED BY CIKGU HUSRITA

9.2 HEAT TRANSFER AND THERMAL EQUILIBRIUM

 Heat flows from objects with high temperature to objects with low temperature

Three different ways heat flows :

Conduction Convection Radiation

Heat flows from a hotter region Heat flows through fluids Heat transfer through vacuum
to a colder region through (liquid or gas) from a hotter (without any medium)
solid
region to a colder region Heat is transferred in the form
Particles that received heat of electromagnetic waves
energy will vibrate at fixed Heat is transferred by the
position and transfer energy to movement of hot particles The heat transfer rate is the
the neighboring particles through convection currents same speed as the speed of

Rate heat transfer is fast The heat transfer rate is slower light
than conduction

CONDUCTION

HEAT TRANSFER THROUGH
SOLID

CONVECTION IN LIQUID

 Convection is the transfer of heat from hot region to cool
region in fluids (liquid or gases) by circulating movement of the
fluids

 The circulating movement of steam of fluid is called a
convention current

• Water begin to xxxxxxxx Convention current • Hotter water

cool when Purple potassium expands
reaching the top permanganate • It becomes less
• It becomes crystal
denser and sink dense and rises

CONVECTION IN AIR

Smouldering Hot air
paper
Cold air
Chimney
Smoke
particles Candle flame
Glass front
Box
Convection in
microwave • Cooler air drawn into
the box to replace hot
air which has escaped • The air above the candle
flame get hot and expands

• The hot air becomes less dense
and rises

RADIATION
 Radiation is the transfer of heat through vacuum in the form

of waves
 Heat from the Sun can only transfer to the Earth by radiation

because space in between them is a vacuum
 The heat is radiated by the sun is via electromagnetic waves

Heat from Moon
the Sun

Sun Earth

HEAT FLOW IN NATURAL PHENOMENA

SEA BREEZE  During the day, the air on land is
warmer compared to the sea
Hot air rises Cold air from the
sea blows in to  Hot air on land expands and
take its place becomes lower in density and
rises up.

 Cold air from the sea blows to
the land to replace the hot air
and produces the sea breeze

The land heats up faster Sea
than the sea

HEAT FLOW IN NATURAL PHENOMENA

LAND BREEZE

Cooler air from Hot air above  At night, the air in the sea becomes
the land blows the sea rises warmer compared to land
in to take its
place  Therefore, the hot air becomes less
dense and rises up
Land Sea
 The cold air from the land blows
towards the sea to replace the hot air
and produces the land breeze

HEAT CONDUCTOR

1. Substances that conduct heat are called conductors of
heat.

2. Some substances conduct heat readily. They are called
good conductors of heat.

3. All metals such as iron, magnesium, aluminium and zinc
are good conductors of heat.

4. The metal that conducts heat best of all is silver. Copper
is next best conductor, followed by aluminium, brass,
zinc, tin, iron and lead, in that order.

HEAT CONDUCTOR

Cooking utensil made The car radiator is made The base of the iron is
from metals to shorten the from metal to ensure fast made from metals to
enable us to iron clothes
cooking process heat flow to the
surroundings faster

Mercury in thermometer is
a good heat conductor. It

can detect change in
temperature very quickly

HEAT INSULATOR

1.Substances that conduct heat poorly are
insulators or called bad conductors of heat.

2.Non-metals such as glass, wood, cork, air,
water and wool re insulators.

3.Fluids, i.e. liquids and gases are poor
conductors of heat.

HEAT INSULATOR

Handle of utensils are The ice box is made from The blanket is made from
made from plastic or polystyrene or fiberglass wool to maintain the body
wood to prevent heat
from reaching the hand to delay the ice from heat by trapping air
melting

Oven gloves that are heat
insulator can prevent your

hands form getting
scalded while taking food

trays out from the oven

THERMAL EQUILIBRIUM

 When two objects of different temperature are in thermal
contact, heat energy transfer happens between the objects

 Heat energy flows from the object with high temperature to the object with low
temperature until thermal equilibrium is reached.

 Thermal equilibrium occurred when heat transfer between two objects is ZERO