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Unit 14 - Assignment 3 - P3
Task 1
Conduction
When an object is heated, the thermal energy is transferred into kinetic energy and the particles
start to vibrate
...
This is because more thermal energy is transferred into kinetic energy
...

Conduction in metals operates very differently; in a metal, electrons are free to move throughout
the metal
...
There is a link between electrical and thermal conductivity in
metals, this is the Wiedemann-Franz Law
...
Any difference is due to the contribution made by the
metal ions acting like an ordinary, non-metallic, solid
...
Once the heat source is removes, convection no longer
occurs
...
Less thermal energy can transfer
into kinetic energy, The air particles do not vibrate as much
...
The air gets heated up again and the cycle starts again
...
When gas is heated it expands, so the same mass now
occupies a much larger volume
...
The less dense air rises up
...
The air particles start to
vibrate, the thermal energy transfers into kinetic energy
...
This is also called infrared radiation
...

Infrared radiation is a electromagnetic radiation as shown in the electromagnetic spectrum
...

Some surfaces are better than other surfaces when reflecting and absorbing infrared radiation
...
A matt black
object would radiate more thermal energy than a white object
...

Colour

Finish

Dark
Light

Dull or matt
Shiny

Task 2

Able to emit thermal
radiation
Good
Poor

Able to absorb
thermal radiation
Good
Poor

Aim: Investigate any one of the factors affecting the rate of heat loss in a liquid
...
After insulation is
applied, the rate at which the heat is lost decreases
...

Control variable- Liquid used, total duration of time, initial temperature of water,
surrounding temperature
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Set up equipment as shown in the first diagram
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Boil water in a kettle
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Pour the boiled water into both the copper calorimeter and the glass beaker
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4
...

5
...

6
...

7
...

8
...
Make sure you
make a lid
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Repeat steps 2-7 again
...

However the difference between initial temperature and final temperature for 'Copper insulated' is
18oC
...
However the difference between initial temperature and final temperature for 'Glass
insulated' is 14oC
...

However, the temperature difference for 'Copper insulated' is higher than the temperature
difference for 'Glass insulated'
...
The
thermal conductivity for glass is 0
...
This means that copper is a much better conductor than glass, glass is an insulator
...
This graph shows that
copper loses more heat when it is not insulated
...
The table
shows that the temperature change for 'Copper uninsulated' is greater
...
This graph shows that
glass loses more heat when it is not insulated
...
The table shows
that the temperature change for 'Glass uninsulated' is greater
...
This is due to the many errors that occurred
in this experiment
...
For example, most of the errors in the
experiments come from inaccurate temperature readings
...
To reduce this error, use an electronic thermometer
as there would be no parallax error and it also read decimal values
...

By using a highly polished calorimeter in the experiment, it will reduce heat loss by radiation
...
This means that
there is a greater heat loss through convection and conduction
...
g
...
It will also mean that
some water would evaporate so that the mass and volume would not be accurate
...
To reduce this error, make sure when making the case
of insulation that the bottom of the container is also insulated
...

Also, the inside of the containers should be painted white, this is so that it would reduce the heat
loss through radiation
...
The outside of the container should also be painted black
...


As the glass beaker and the coper calorimeter are differently shaped to each other
...
Also, the glass is slightly thicker than the
copper, which means it is an even greater insulator and would reduce the rate of heat loss
...
This means that the uninsulated glass
would has lost heat more through convection than the copper calorimeter
...
This means that there could have been an
error of the water cooling at different rates because of this factor
...
This is to reduce the error of the mass of the water, having a significant change on what the
results should be
...


A hot water storage tank is a water tank which is used for hot water storage for space heating or
domestic use
...
Hot water tanks may have a built-in gas
or oil burner system, or electric immersion heaters
...
Insulation is commonly
used on the hot water tank
...
It is important that the blanket is the right size for the tank so that
conduction (through the air) and convection does not occur
...

Hot water tanks heat up loads of water in the morning, having hot water in the morning, then later
through the day, heat is lost
...
However, if
the water runs out, you would have to wait till the next day for more hot water
...
This means that more energy is required to heat up or cool down the
water
...
However, as the hot water tank has a bigger surface area, it loses heat faster
...
This is because there is more particles which absorb the heat from the tank
...
As the floor is a greater conductor than the air, it will pass on the heat energy
more as the particles are much more closer together
...
In a gas, the particles are much more
spread out
...

To reduce heat loss through radiation, the outside of the hot water tank would normally be painted
black
...
The white/silver surface would reflect the
infrared radiation back into the container
...

The insulating material around the hot water tank would be more secure and properly applied
around the tank
...
Heat loss can also occur through the water
pipes through conduction
...
However, there may be insulation wrapped around the pipes to
reduce heat loss through conduction
...
The small
gap between the two panes of
glass is filled with air
...
Air is not a good
conductor of heat
...
The
amount of heat loss through the
walls can be reduced
...
This therefore reduces
the heat loss through conduction
...
this can be
done by laying loft insulation
...
This is done
by laying loft insulation
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Use carpets instead of tiles and
floorboards
...
It prevents conduction
as air is trapped between the
fibres
...

Fibreglass roof insulation prevents
heat loss through conduction and
convection
...
This would
reduce heat loss through
convection
...
Heat
transfer by convection
currents is reduced by
making the gap between
the two panes of glass
narrow
...
This material
that the insulation is made
of will prevent air
circulating inside the cavity,
which reduces heat loss by
convection
...
This would reflect
the heat back into the room,
instead of it being lost
through the walls
...

Install tinted windows to trap
heat inside the classrooms
...


Use energy saving lightbulbs
...
90%
of the energy is wasted
through thermal energy, with
only 10% transferred to light
energy
...

Install roof insulation
...
This would also
circulating inside the cavity, reduce the amount of energy
which reduces heat loss by used to power the light bulb
...

This would reduce heat loss
through radiation through
the walls
...
Put foil behind radiators to
Fibreglass roof insulation
reflect the heat back into the
prevents heat loss through room
...
loss through radiation
It prevents conduction as
through the walls
...


Put up curtains
...


fibres and convection is
prevented as warm air
cannot rise up out of the
roof
...

This would reduce heat loss
through radiation through
the walls
...
a) Q/t = kA (T1 - T2) / L
0
...
5 (18 - 12) / 0
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8 * 1
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005 = 4320W

c)

The rate of heat flow would decrease if the number that the value would be divided by is increased
...
Also, if the temperature outside is lesser, than the rate of heat flow would be greater
...
This is
shown in the calculations for '1a' and '1b'
...
Q/t = kA (T1-T2) / L
a) 238 * 0
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005 = 249,900W = 249
...
025 (200 - 25) / 0
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875W = 210
...
030 (200 - 25) / 0
...
7KW
This means that aluminium has the greatest rate of heat energy from the hotplate to what is in the
pan
...


1(5
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15 * 1018) * (6000)4 = 4
...


= 2047K

5
...
7 * 10-8) * (12,000)4 = 1,181,952,000W = 1,181
...
7 * 10-8) * (3,100)4 = 5,264,069
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3MW

6
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78 = 2022K

Unit 14 - Assignment 3 - D3
Heat transfer
Solids
When an object is heated, the thermal energy is transferred into kinetic energy and the particles
start to vibrate
...
This is because more thermal energy is transferred into kinetic energy
...

Conduction in metals operates very differently; in a metal, electrons are free to move throughout
the metal
...
There is a link between electrical and thermal conductivity in
metals, this is the Wiedemann-Franz Law
...
Any difference is due to the contribution made by the
metal ions acting like an ordinary, non-metallic, solid
...
Particles
are not involved in radiation
...
This is

also called infrared radiation
...
Some surfaces are better than other surfaces when reflecting and absorbing infrared
radiation
...
A

matt black object would radiate more thermal energy than a white object
...


A microwave uses radiation to transfer heat to the food/drink that is in the microwave
...
Microwaves are a type of wave that are in
between radio waves and infrared radiation on the electromagnetic spectrum
...
It also has higher frequencies and
shorter wavelengths than radio waves
...
45 gigahertz
...
Once absorbed, they are converted directly into atomic motion, i
...
heat
...

Microwave radiation cooks foods much faster than infrared radiation because it penetrates foods
several inches deep, unlike infrared which is mainly absorbed at the surface
...
Metal reflects microwaves; this is why metal pans do not work
well in a microwave oven
...

Meats cooked in a microwave oven lose greater amounts of moisture and easily become dry
...

A waveguide (this is hidden in the wall to direct the energy to the food)
...


At a molecular level, heat is the transfer of energy by temperature differences; at the microscale, it
is the increased motion of molecules
...
This
means that the whole mass of the food can be cooked simultaneously
...
To give the
molecules more energy, it is exposed to electromagnetic waves (microwaves) that emanate from the
tube
...
Water will try to
align with the radiation's electric field
...


Liquids
Conduction in liquids uses kinetic energy of one particle being passed to another which it is next to
...
This process repeats particle after particle,
allowing thermal energy to be passed
...
However,
heat transfer through convection is a much more efficient method for liquids
...
Once the heat source is removes, convection no longer
occurs
...
Less thermal energy can transfer
into kinetic energy, The air particles do not vibrate as much
...
The air gets heated up again and the cycle starts again
...
When gas is heated it expands, so the same mass now
occupies a much larger volume
...
The less dense air rises up
...
The air particles start to
vibrate, the thermal energy transfers into kinetic energy
...
A highly insulated tank can stay hot for days
...

First the hot water tank is supplied with electrical energy
...
The heat pump sends a signal to close the
contactor
...
This then converts into thermal energy
...
This then causes
the heat to turn on
...
This causes the heat to turn off
...
After the
water is heated, it exits the tank via a vent through a tube to the tap
...
The hotter the particle is, the faster is will vibrate, thus transferring the
thermal energy from the heating element, to the water
...


Gases
Conduction in gases can take occur, however it is very slow
...
If the temperature difference
between hot and cold is quiet small, the gas can remain stationary
...

Convection only occurs in liquids and gases
...
Away from the heat source, the air has less thermal energy
...
The air becomes more dense than the
surrounding air and sinks down
...
This is called
a convection current which transfers energy
...
Therefore, its density decreases
...
As the
particles spread out, the air becomes less dense than the surrounding air
...


Convection oven: Convection occurs in convection ovens
...
The principle of convection relies on the circulating
air; this transfers heat to the food as it moves around the food
...
There is also a fan which
sucks air from the oven chamber, past the heating element and back in to the oven
...
The heat causes
particles which are nearest to the source of heat to vibrate
...
This is then caused by
the gas particles vibrating against the surface of the food
...
By this
method, the food is cooked evenly as hot air is distributed throughout the oven chamber
...
A
conventional oven only has the top and bottom heating element
...


Bibliography:
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•
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http://www
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co
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sht
ml
http://www
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com/Q/What_is_the_difference_between_bulk_motion_and_wave_m
otion
Annets F, Foale S, Hartley J, Hocking S, Hudson L, Kelly T, Llewellyn R, Musa I and
Sorensen J – BTEC Level 3 National Applied Science Student Book (Pearson, 2010)
ISBN 9781846906800



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