Notes

TEMPERATURE:
-Temperature is a measure of how hot to cold and object is.
-Temperature is measured in degrees Celsius (oC).
-The instrument used to measure temperature is a thermometer.
Colour: Temperature in oC:
White = 1500
Yellow = 1000
Orange = 700
Red = 500
To make an object hotter you need to give it heat/thermal energy. Thermal energy travels by one of three ways:
-Conduction
-Convection
-Radiation
THE KELVIN SCALE:
-In the nineteenth century an Englishman, Lord Kelvin decided it was inconvenient to use negative numbers when measuring cold temperatures.
-The Kelvin Scale, like the Celsius scale, is based on two fixed points, freezing point and boiling point.
-The starting point of the Kelvin scale is called absolute zero. This is the temperature at which all the particles have cooled down and stopped moving.
-The boiling point of water is 373K = 100oC. 0K = -273oC.
EVERYDAY TEMPERATURES:
-Frozen food is kept at -30oC.
-Ice forms at 0oC.
-Fridge is kept at 5oC.
-Room temperature is usually 20oC.
-A baby's bathwater should be 35oC.
-Body temperature is 36.5oC.
-Milk is pasteurised at 70oC.
-Water boils at 100oC.
CONDUCTION:
-A conductor is a material that lets energy flow through it, low resistance.
-Conduction happens best in solids because the atoms are compact, energy moves through the vibrations.
-An example of a material that is a good conductor would be metal, the denser the better.
-Materials that are good conductors often feel cold when we touch them. This is because they are conducting the heat away from our hands and bodies. Therefore, the better the conductor, the cooler it feels.
INSULATORS:
-An insulator is a material that doesn't let energy flow through it, high resistance.
-Some examples of materials that are good insulators would be birds feathers, wood and clothing, they all have pockets of trapped air.
CONVECTION:
-Thermal energy cannot travel through water or air by conduction, as both are bad conductors.
-Convection takes place whenever one part of a liquid or gas is heated more than the rest. The molecules in this heated part have more energy than the cooler molecules and therefore move around more. These molecules spread out and this part of the gas or liquid be ones less dense than that around it. As a result they rise and cool, and subsequently become denser, liquid or gas sinks down to take its place. These movements of warm, less dense air or liquid molecules moving upwards, and the cooler, more dense air or liquid molecules moving downwards is called convection currents.
Kettle/Room:
The heating element heats the water/air next to it. This hot water/air expands and becomes less dense and rises. The cooler water/air at the top is denser and sinks, and then is also heated by the heating element. This cycle continues until all the water/air is heated.
RADIATION:
-When your that your bread under the grill, the heats travels downwards from the grill to the bread. This thermal energy cannot travel through convection at convection carries heat up not down. It can't travel through conduction either as the air between the bread and grill is a bad conductor. So we use a process called radiation.
-Everything gives off heat radiation. This is also known as infra-red radiation.
-Infra-red radiation is used in some burglar alarms, in infra-red cameras to locate people under rubble, also in night sight cameras and lenses.
-The hotter the object, the more infra-red radiation it gives off.
-The amount of radiation given off by an object also depends on the colour to its surface:
Best emitter = dull/dark colour (black)
Worst emitter = light/shiny colour (silver/white)
Best absorber = dull/dark colour (black)
Worst absorber = light/shiny colour (silver/white)
Best reflector = light/shiny colour (silver/white)
Worst reflector = dull/dark colour (black)
SAVING HEAT ENERGY:
-The main areas of the house that we loose heat from are (and ways we can insulate them):
1. Walls (cavity wall insulation = polystyrene, sheep's wool or air).
2. Roof (loft insulation = rock wool).
3. Doors (draught excluders).
4. Floor (insulation under floor = polystyrene under concrete, or carpets).
5. Windows (double or triple glazing).