L2 - Temperature 1

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A temperature scale is a range of numbers for measuring the level of hotness.
Everyday temperatures are normally measured on the Celsius scale (sometimes called the 'centigrade’ scale).
Its unit of temperature is the degree Celsius.
The numbers on the scale were specially chosen so that pure ice melts at 0 °C and pure water boils at 100 (under standard atmospheric pressure of 101 325 pascals).
These are its two fixed points. Temperatures below 0 have negative (-) values.

Temperature is measured using a thermometer. One simple type is shown below. The glass bulb contains a liquid - either mercury or coloured alcohol which expands when the temperature rises and pushes a 'thread' of liquid further along the scale.

Every thermometer depends on some property (characteristic) of a material that varies with temperature. For example, the thermometer above contains a liquid whose volume increases with temperature.
The two thermometers next use materials whose electrical properties vary with temperature.
All thermometers agree at the fixed points. However, at other temperatures, they may not agree exactly because their chosen properties may not vary with temperature in quite the same way.

In any object, the particles (atoms or molecules) are moving, so they have kinetic energy. They move at varying speeds, but the higher the temperature, then on average - the faster they move.
If a hot object is placed in contact with a cold one, as on the right, there is a transfer of thermal energy from one to the other. As the hot object cools down, its particles lose kinetic energy. As the cold object heats up, it particles gain kinetic energy.
When both objects reach the same temperature, the transfer of energy stops because the average kinetic energy per particle is the same in both:
Objects at the same temperature have the same average kinetic energy per particle. The higher the temperature, the greater the average kinetic energy per particle.

Temperature is not the same as heat. For example, a spoonful of boiling water has exactly the same temperature (100 °C) as a saucepanful of boiling water, but you could get far less thermal energy (heat) from it.

As the temperature falls, the particles in a material lose kinetic energy and move more and more slowly. At -273 °C, they can go no slower. This is the lowest temperature there is, and it is called absolute zero.
The rules of atomic physics do not allow particles to have zero energy, but at absolute zero they would have the minimum energy possible.
In scientific work, temperatures are often measured using the Kelvin scale.
Its temperature unit, the kelvin (K), is the same size as the degree Celsius, but the scale uses absolute zero as its zero (0 K). You convert from one scale to the other like this:

5.02---Temperature-1.docx

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