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Topic 1 how is heat transferred?


Heat Flow
Objects get hot if heat energy (thermal energy) passes into them. We know they get hot because
the temperature rises. It is important that we know the difference between temperature and
heat:
Temperature - the measure of how hot something is, measured…

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If we apply heat, the molecules vibrate with bigger vibrations and set their neighbours vibrating
with bigger vibrations. These pass on the vibrations to their neighbours in turn. The bigger the
vibrations, the hotter the material. If the vibrations are passed on easily, the material is a good
conductor. (In…

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Energy can neither be created nor destroyed.
It is only transferred from one form to another.


What this means is that you cannot get something for nothing. Nor can you lose it. Every joule of
energy has to be accounted for. This is what this topic is about.

Useful Energy…

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In this system the vehicle uses a generator to charge up a battery. When the vehicle accelerates,
the battery gives power to a motor.

Low Grade Heat
There are ways of recovering waste heat. Many devices have heat exchangers which use waste
heat going out to warm up air or…

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The energy efficiency is always a fraction less than 1, which is multiplied by 100 to give a
percentage. (If you get 2/3 correct in you exam, you get 67 %.)
Examples of efficiency:
Device Efficiency (%)

Steam engine 10

Car 35

Power station 45

Electric motor 70

Transformer 95…

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To do a useful job for us, electrical energy has to be converted into other forms of energy. For
example:

A drill:

Electrical Energy Movement (Kinetic) Energy


A radio:

Electrical Energy Sound Energy


Appliance Useful Energy Other Energy

Drill Kinetic Noise/heat

Iron Heat Heat (surroundings)

Hoover Kinetic (moving Air) Heat/Noise…

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TV set 200 0.20

Kettle 2200 2.2

Shower 7500 7.5

How much does it cost to use an appliance?
When we work out the cost of using an appliance, we pay for the energy that has been used. We
could pay for the number of joules used, but the joule…

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How much does Lorraine's shower cost?

Lorraine has used 2.5 kWh
Cost = 2.5 kWh × 8 p = 20 pence

How do we get electricity to our homes?
Electrical energy cannot be stored as electricity. In a battery it is converted to chemical energy.
We are constantly using electricity,…

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Why High Voltage ?
The reason for voltage being so high is that the current is lower. Therefore the wires can be
thinner, and don't get so hot. Therefore less energy is wasted. Even so there is a fair amount of
energy lost in heating up the wires which heats…

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To make the power station more efficient, the steam is cooled in a condenser (6). The waste
heat is carried to the cooling tower (7), where it returns as cool water (8). The clouds you see
around cooling towers are not smoke; they are water vapour.
The energy chain in…

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