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Heat
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Temperature
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Do NOT confuse the two - they are linked but NOT the same.
 Input
of heat to a system usually results in an increase of temperature but NOT where there is a change of state involved - see latent
heat
High temperature of an object does not necessarily mean a lot of heat has been given to it. Heat a thimble of water until it boils and then give the same amount of heat to a bath of water - you won't even detect a change in temperature in the bath of water!
How much heat energy is needed to raise the temperature of 1kg of a substance is called the specific heat capacity. The SHC helps us compare how easy it is to heat up different substances.
Experiments that investigate heat transfer between substances is called calorimetry
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| Heat
is a form of energy. |
Temperature
is a measure of how hot or cold things are. |
|
Difference
in temperature makes heat energy move from a hot part to a cold
part of an object.
|
| It
is measured in joules (J). |
It is measured in
degrees.
The Celsius and
kelvin scales of temperature are used in science but there are
others such as centigrade and fahrenheit.
Try the Dalek
temperature scale!
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| |
Pure
ice melts at 0oC or 273K |
| |
Pure
water boils at 100oC or 373K at Sea Level - see here for what happens at different altitudes |
| It
can be measured with a joule-meter or a combination of instruments,
the readings of which can be used to perform a calculation to establish
the value. |
It
is measured with a thermometer. |
| |
There are many different
kinds of thermometer, their range, sensitivity and constuction
varies widely.
A thermometer can
be made from anything which responds to temperature change.
You should know
about the liquid in glass thermometer
in detail. This uses expansion of liquids with temperature rise.
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| Heat
always flows from hot areas to cold areas (See U-values ) |
|
| The
bigger the difference in temperature between two objects the faster
the heat will move (See the pressure cooker ) |
|
| The
bigger the area of contact between the two objects the faster the
heat transfer will happen |
|
| Heat
moves easily through good conductors of heat (such as metals) and
very slowly through heat insulators (such as trapped air pockets, wood or plastic). See double glazing and cavity wall insulation. |
The
temperature of an object made of a good conductor of heat tends
to be the same throughout the object but an insulator will be much
hotter near the heat source than it is elsewhere. |
Heat
radiation is absorbed/emitted readily
by dark, dull, rough surfaces and less easily by light, shiny,
smooth surfaces. |
The
temperature of dark, dull, rough surfaces will rise quickly if irradiated
with infra red heat radiation and light,
shiny, smooth surfaces will not respond as quickly. The hot surfaces
will then cool at a similar rate to the way they rose in temperature
when the heat source is taken away. |
| There
are three methods of heat transfer: conduction,
convection and radiation |
As
temperature rises an object usually expands. Click here
for a question sheet on expansion. |
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