Whether you want to prevent heat from escaping, cook something more quickly or answer an exam question, you need to know the processes of heat transfer:
- conduction
- convection
- radiation
It's also worth a look at the Thermal concepts page for information about evaporation.
While all matter is capable of allowing heat transfer by conduction, it is fastest in solids, particularly in metals with delocalised electrons.
When the end of a solid bar is heated, the particles are made to vibrate more than before. The kinetic energy is passed from one molecule to the next along the rod by collisions.
NB: Remember that all objects above absolute zero will have at least some kinetic energy in their particles.
We don't ask you to memorise much in Phyiscs, but it's worth learning the key words for a good convection answer...
When a fluid is heated, the molecules spread apart, causing it to be less dense. This less dense fluid rises into the surrounding cold fluid. This leaves a region of low pressure behind and so the cooler, denser fluid fills the gap, creating a convection current.
Radiation is what you feel as you warm your hands in front of a fire.
All objects with a temperature above absolute zero emit infrared radiation. Infrared radiation is a region of the electromagnetic spectrum, and so it travels at the speed of light through a vacuum (convenient for planet Earth!) as well as being able to pass through air and other matter.
The amount of radiated heat depends upon the temperature of the source, it's colour and surface area. The rate of radiation absorbed by and emitted from black bodies is greater than silver ones (which are much better reflectors). Hot objects emit more radiation than cooler objects.
Use quizzes to practise application of theory.
START QUIZ!
When a solid changes to a liquid energy is required.
Which is the best description of where that energy goes.
Chemists talk about breaking bonds we talk about increasing PE, it would also be bonds between the molecules rather than atoms but I'd rather not get into that.
Temperature doesn't change so no change in KE
Water molecules actually get closer.
100g ice is melted at 0°C in 5 minutes by an electric heater.
The latent heat of fusion of ice is approximately 3 x 105 Jkg-1
The amount of heat required to melt the ice = kJ
The power of the heater = W
Q = mL, P = Q/t careful with units
The temperature is measured as some water is boiled in a 2kW electric kettle.
The latent heat of vaporisation of water is about 2 x 106 Jkg-1
Temperature T = °C
The heat required to boil the water = kJ
The mass of water = kg
Q = Pt
m=Q/L
If you get melted sugar on your skin it burns very badly.
Fill the gaps to give the explanation.
Word list: constant, energy, solid, liquid, temperature, release, state, power
When sugar changes from to it must release , if in contact with your skin this will be given to you. remains constant as the sugar changes so it remains at melting point until all the is released. during this time the sugar will be damaging your skin.
It does too.
A type of salt is used to store solar energy collected in the day time so it can be used at night. The power station collects 1 MW.
The latent heat of fusion of the salt is 3 x 106 Jkg-1
The energy collected in 10 hours of sun light = MJ (no commas)
The mass of salt melted in one day (10 hours of sunlight) = kg
MJ is 106 J
Consider a frozen chicken. To defrost the chicken, you have two options: placing it on the worktop as it is, or wrapping it in a woollen jumper. Which option will be the quicker?
How much of Heat transfer have you understood?
Twitter 
Facebook 
LinkedIn