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P1a 1
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Infra-red, from the
sun, can pass through both the atmosphere and the vacuum of space
...

It is the only way in which heat can reach us from the sun
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The hotter or darker, an object - the more I
...
radiation it will
emit
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R
...

Is an electromagnetic wave
...
The short wavelength energy
is (i) absorbed by whatever it comes into contact with and (ii) is re-emitted as a longer
wavelength form of energy
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P1a 1
...

Back of fridge
Car radiator

Good emitters

Vacuum flask

Poor emitters

↕

Black
Dull
White
Shiny

Good absorbers

↕

Poor absorbers

Solar panel

Different colours
of paint on cars
Mirror

Which surfaces are the best absorbers of radiation?
Matt surfaces absorb radiant energy more than shiny
surfaces
...


Demonstration:

Grammar Physics

Energy transfer

Page 2 of 13

P1a 1
...
Whereas……
...
E
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Solid: Zero Kelvin (OK) atoms are stationary
In a solid, particles are held next to each other in fixed positions
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A solid
will keep it’s shape
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E
...
E
...

Liquid
...

On heating molecules
and gain K
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- move faster

- move further apart (5%)

Boiling: liquid to gas Molecules gain P
...
(temperature constant move x 10 further
apart)
...
The molecules are much further apart and move much faster
and in random directions
...

On heating molecules
Solids and liquids

Liquids and gases
Solids and gases

- move much faster only
Similarities

Molecules are close together;
State is incompressible
Molecules are free to move, flow
none

Differences

S - fixed positions
L - free to move
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Heat always travels from hot areas to cooler areas
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Grammar Physics

Energy transfer

Page 3 of 13

Summary:

(Summary questions page 29)
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Boiling – occurs at the boiling point and throughout the liquid
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4

Conduction

Pages 30/31

Conduction – is the main way that heat travels through solids

Heat
Conduction in non-metals





-

Non metals are poor conductors of heat
...

As they vibrate, they collide with other atoms, causing them to vibrate
...

In a non metal all electrons are firmly bound to their atoms
...
They contain free electrons
which, on heating move quickly (diffuse) through the solid colliding with ions and other
electrons, and hence passing on the heat (or k
...
) energy (large part of process)
...
)

Liquids and gases are very poor conductors of heat
...
g
...

Copper is

6
600
7200
18000

x better conductor than iron
x better conductor than glass
x better conductor than water
x better conductor than air
...
g
...
0 mins and check the temperature rise
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Question: Why does the insulation not burn or become damaged?

………………………………………………………………………………………………………
...

glass
A
poor
conductor

2
...


Flame
Cu gauze

Copper feels warmer quicker than glass
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Davy safety lamp
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Ice remains frozen as water boils
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5

Convection

(Summary questions page 31)
...

On heating a fluid the molecules, move faster and so move further apart – become
less dense – and rise
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smouldering
paper

Convection of Gases

Natural convection currents, called thermals, can form above hot pieces of land
...

Convection currents are responsible for creating all of our weather patterns, as well as
being the driving force behind continental drift
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Sea breezes - warm air above the
ground rises and cooler air from the sea
moves in to replace it
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Grammar Physics

Energy transfer

Page 6 of 13

P1a 1
...


The energy of the particle changes in a collision
...


The temperature of a liquid is related to the average energy of each molecule
...


If they are also near the surface, these high energy molecules will escape from the liquid evaporate
...


Even at a temperature well below its boiling point, some of the liquid molecules will be
able to escape
...
the surface area

Hang clothes on the line

2
...


3
...


More molecules with enough energy/speed to escape
...

Boiling – occurs at the boiling point and takes place through out the liquid
...
The temperature falls and energy
flows in from the outside, e
...
the water
under the beaker
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g
...
This will be affected by:
(i) The area of the mirror and (ii) The temperature of the mirror (lower if better)
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Grammar Physics

Energy transfer

Page 7 of 13

P1a 1
...
g
...

The radiator is made of metal, so heat can be conducted quickly away from the
hot water
...
This increases the flow of air (forced convection) through the radiator
and so also the cooling effect
...
B
...
g
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A computer heat sink and a good old fashioned Harley Davidson machine!

The vacuum flask
...

The vacuum flask is designed to
keep things hot or cold
...

I
...
Radiation is reduced by the
silvered surfaces
...

The glass walls are very thin
...

So a hot liquid will eventually cool down because, in practice, (i) radiation does occur
slowly at the silvered surfaces; (ii) Conduction through the cap, glass and pads
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g
...
g
...

The material in contact with the object (e
...
solid liquid or gas)
...




Consider the desert and arctic foxes with their large and little ears!!!

The quickest transfer of heat will occur with the largest temperature difference, largest
area and the largest amount of material (e
...
fan blowing air through a car radiator) passing over
the object
...

Since the temperature difference between an object and its surroundings affects the rate
of transfer of heat, then:
 The tea and mug will cool fastest when the tea is hottest and
 As the tea cools down, the rate of transfer of heat to the surroundings will also
decrease
...

(Summary questions page 37)
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8

Specific Heat capacity

Pages 38/39

The temperature rise for a substance, on being
heated, depends on:
1
...

2
...

3
...


Specific Heat capacity – of a substance is the
energy required to raise the temperature of 1kg
of the substance by 1oC
...

Water has a very large shc – compare it to other materials shown in the table
...

………………………………………………………………………………………………………
...
If the initial temp = 14 oC, and the final temperature is
22 oC, calculate the shc for aluminum
...
Their shc value is reasonably large – so they can store a lot of heat energy, and
being an insulator, they give out heat slowly over a period of hours
...

Grammar Physics

Energy transfer

Page 10 of 13

Further space for SHC calculations as required:

P1a 1
...

The U-value of a material is a measure of the
energy passing through 1m2, every second, for a
temperature difference of 1oC
...


In practice a vacuum is not used between the glass panels, because it will leak with time
...

Black – absorbs IR radiation, metal – good conductor, (free electrons) and low shc
so heats quickly
...

Process - the plate heats up and this heat energy conducts through the metal to
the water in the copper pipes (joined to the plate)
...

in a simplified
system, it moves by
natural convection to
a storage tank placed
above the solar panel
...

The solar panel, with
the glass case acts like
a miniature ‘green
house’
...
Why
antifreeze?

……………………………………………………………………………………………………
……………………………………………………………………………………………………


Solar panels are expensive to install, very cheap to run and need to be located in
places with lots of good strong sunshine!

Grammar Physics

Energy transfer

Page 12 of 13

Example: Fridge – Explain how it works using, conduction, convection, radiation and
within the liquid by evaporation and condensation!!!

Evaporation: The compressed liquid passes through the ‘narrow hole’ and evaporates
causing a huge cooling effect
...

Condensation: The vapour is compressed, by the pump, in the high pressure pipe and
so is forced to condense and gets very hot! (a liquid, remember, has less energy than in
its gas state)
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Convection 1: Air, at the back hits the hot pipes and fins, becomes less dense and rises
and so cools the back of the fridge
...
The air
then hits the food and being less dense rises
...
R
...

(Summary questions page 41)

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