4. Heat is the transfer of thermal
energy from a hotter region to
a colder region.

6. It is the amount of heat energy needed to
change the temperature of a substance by 1
Kelvin (or 1C).
Formula:
unit of heat capacity: J/K
Where
C = heat capacity (J/K)
Q = Amount of heat energy (J)
Δθ = change in temperature (K)

8. It is the amount heat energy needed to change the
temperature of 1 kg of a substance by 1K (or 1C).
Formula:
unit of specific heat capacity: J/kgK
Where
c = specific heat capacity (J/kgK)
Q = Amount of heat energy (J)
Δθ = change in temperature (K)

10. Apparatus: an aluminum block, heater, thermometer,
stopwatch, ammeter, voltmeter.
Method:
1. Record the mass of the aluminum block and its initial
temperature.
2. Start the heater and the stopwatch simultaneously.
3. Take the ammeter and voltmeter readings.
4. Record the final temperature of the block.
5. Use the formula given below to calculate the specific
heat capacity of the aluminum.
Formula:
C= VIt
mΔ
Where
V = voltage (V)
I = current (A)
t = time (s)
m =mass of the aluminium block (kg)
Δ = change in temperature (C)
c = specific heat capacity of aluminium (J/kg/K)

15. •On heating, a solid changes to a liquid. We call this change
of state ‘Melting’.
•During melting, heat energy is used to break the bonds
between the molecules of the solid.
•Melting will occur once these molecular bonds are broken
and they move away from their previously fixed positions.
•There is no change in temperature of the body during
melting, even when heat is continuously being supplied to
the body. Temperature of the body will increase when all the
bonds are broken.
•Heat that is absorbed to break these bonds without a change
in temperature is called latent heat of fusion.
•Applying pressure on ice will cause its melting point to drop.

16. From A --- B: Temperature of ice rises from -15C to 0C.
From B --- C: No change in temperature as heat is being absorbed.
At this stage, it contains a mixture of ice and water.
From C --- onwards: Temperature starts to increase as now all the
ice has melted. Energy is now used to increase the temperature of
water.

17. •The process by which a liquid changes its state to become a
solid when heat is removed from a body.
•When a body undergoes solidification, heat is released as
intermolecular bonds are formed. This results in a body more
rigid as compared to that of the liquid.
•Despite heat being given off during solidification, there is no
change in temperature.
•Temperature of the body will only start to drop when it is
completely solidified or has the same solid state throughout
the entire body.

18. From A --- B: Temperature of water falls from 100C to 0C.
From B --- C: No change in temperature as heat is being released. At
this stage, it contains a mixture of ice and water.
From C --- D: Temperature starts to decrease as now all the water
has solidified.

20. •Condensation is the change of gas to liquid.
• Heat energy is given out as gas particles
slow down and move closer to one another
to form liquid.
•Sublimation is the change of solid to gas
without melting.
•Heat is absorbed.

22. •Evaporation is the change of liquid to gas without
boiling, occurs below boiling point on water surface. It gives
cooling effect , as heat energy is absorbed from
surroundings.
•Boiling and evaporating are not the same.
•Boiling only occurs at at a fixed temperature whereas
evaporation takes place at any temperature.
•Boiling takes place within the liquid whereas evaporation
only takes place at the surface.
•Evaporation will cause an object to loose heat and cool
down whereas temperature remains steady when boiling
takes place.
•Boiling produces effervescence whereas evaporation does
not.

23. Factor Its effect on rate of evaporation
1. Temperature The higher the temperature, the faster the rate
of evaporation.
2. Humidity The higher the humidity in the surroundings,
the slower the rate.
3. Surface area The larger the surface area of the liquid, the
faster the rate.
4. Air movement Air blowing will remove the layer of saturated
vapour and hence increase the rate.
5. Pressure Reducing pressure increases the rate.
6. Nature of liquid The lower the B.p, the higher the rate.

26. This is the method of heat transfer in solids.
•It occurs mostly in solids, for example in metals like iron and
copper.
•Conduction is the process of heat transfer that occurs
between atoms or particles that are vibrating in their fixed
positions.
•For example, when one end of a metal rod is heated, the
particles on the heated end gain energy and start to vibrate
faster. They then collide with the less energetic neighboring
particles, causing them to vibrate together.
•Through vibrations of the particles, heat energy is transferred
from the hotter end of the rod to the colder end until an
equilibrium temperature is attained.
•Conduction also occurs in non-metals, such as wood.

27. This is the method of heat transfer in solids.
•Whether a material is a good conductor or poor conductor
of heat depends on the thermal conductivity of that
material.
•A material with a high value of conductivity will be a better
conductor of heat.
•For example, metals are better conductors of heat
compared to wood and air because metals have higher
thermal conductivity.
•Solids like metals are good conductors of electricity and
heat because they have free electrons that move relatively
easily in the metal itself.
•These electrons move in a very high speed, and being
energized, they carry kinetic energy and will collide with
neighboring atoms or molecules.
•This explains why metals are better conductors compared
to non-metals.

28. This is the method of heat transfer in solids.
•Trapping a layer of air to
reduce the amount of heat lost
to the cold environment to
keep our body warm.
•Use of metals such as
aluminum and stainless steel
as cooking utensils and sauce
pans.
•Use of insulating materials
such as wood for handles of
cooking utensils to reduce
amount of heat flow.

30. •It occurs mostly in fluids such as air or water.
•When a glass of liquid, such as water, is heated from the
bottom, the layer of water closer to the heat source expands
and hence becomes less dense compared to the water layer
above it.
•As we know that a less dense object will float above a denser
object.
•Hence the warmer water layer will rise above the colder layer
of water and cause a current to be generated in the glass of
water.
•The process of heat transfer from one region to another
through the movement of heated particles is known as
convection.
•Convection cannot occur in solids because the particles are in
fixed positions and are unable to move freely.

31. This is the method of heat transfer in solids.
•Heating coil of an electric kettle is
placed at the bottom to allow
convection currents to form and
heat up the water.
•Air conditioners are always fixed
close to the ceiling as cold air sinks.

33. •Unlike conduction and convection which require a medium to
travel, radiation can transfer heat through a vacuum.
•It is the only way heat can be transferred in a through a
vacuum.
•It is the process whereby heat energy is transmitted in the
form of electromagnetic waves or Infrared radiation.
•One common example is the heat from the sun which travels
through a vacuum before arriving on earth’s surface.
•Factors that affect the rate of emitting and absorbing
radiation are the colour, shininess and area of the material.
•A dull and dark coloured object is a better emitter and
absorber of radiation compared to a shiny and bright
coloured object.

34. This is the method of heat transfer in solids.
•On a hot day, we should try to
wear clothes of brighter colours
instead of dull and dark colours to
reflect most of the radiant heat.
•Exposing our skin for very long to
harmful UV radiation from the Sun
may cause skin cancer.
•Plants are kept in a greenhouse
which traps heat. the glass panels
will allow shorter wavelengths of
radiation and will trap the
reflected radiation with longer
wavelengths.

36. A vacuum flask is able to reduce heat
loss (to the surrounding) by minimizing
heat loss in 4 possible ways;
conduction, convection, radiation and
evaporation.
1. Conduction and convection through
the sides of the flask are prevented by
the vacuum between the double-glass
walls of the flask.
2. Conduction through the trapped air
above the liquid is minimal since air is
a very poor conductor of heat and the
stopper too is made up of plastic.
3. Convection and evaporation can only
occur when the stopper is removed
during use.
4. Heat loss by radiation is harder to
stop as radiant heat can pass through
a vacuum. to minimize heat loss
through it , the walls of the glass are
silvered so as to reflect the radiant
heat back into the liquid.