How can heat be transferred?
Through radiation, convection and conduction.
Surfaces for absorbing heat:
Dark matt surfaces are better at absorbing heat energy than light shiny surfaces.
Dark matt surfaces are good at emitting heat and absorbing heat, whereas light shiny surfaces are poor at emitting and absorbing.
Infrared radiation:
All objects emit (give out) and absorb (take in) thermal radiation.
The hotter an object is, the more infrared radiation it emits.
Can radiation travel through a vacuum?
Yes.
What is kinetic theory?
The theory explains the properties of different states of matter. (solid, liquid and gas). Solid: close together, regular pattern. vibrate around a fixed position. Liquid: Close together, random. Move around each other. Gas: Far apart, random. Move quickly in any direction.
Conductors:
Non metals and gases are usually poor conductors of heat, these materials are called insulators.
How heat is conducted through a metal:
-The heat is applied to the metal
-The particles in that area gain more energy and start to vibrate MORE vigorously
-The vibrations spread through the metal, conducting the heat all the way along through the metal
FREE Electrons in the metal transfer the KINETIC ENERGY from the hot parts of the metal to the cooler parts, and collide with ions as they travel through the metal
When and what with does convection occur?
Convection occurs in gases and liquids.
A convection current forms when hotter, less dense air rises and cooler, more dense air sinks.
What is evaporation?
Evaporation involves a liquid changing into a gas.
What is condensation?
Condensation involves changing a gas into a liquid.
How evaporation happens:
- Particles in a liquid have different energies
- Some will have enough energy to escape from the liquid and become a gas
- The remaining particles in a liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens.
- This is why sweat cools you down.
How condensation happens:
- Particles in a gas have different energies
- Some may not have enough energy to remain as separate particles, particularly if the gas is cooled down
- They come close together and form bonds between them, releasing energy
- This is why your skin scalds, as when steam touches your skin the energy is released
Factors affecting the rate of condensation:
-The rate of condensation increases if the temperature of the gas is decreased
-The rate of evaporation increases if the temperature of the liquid is increased
-It is also increased if:
The surface area of the liquid is increased
Air is moving over the surface of the liquid (e.g. wind)
Factors affecting heat transfer:
- Surface area and volume of the object
- Material used to make the object
- Nature of the surface that the object is touching
What is U value?
U-value measures the effectiveness of a material as an insulator in buildings.
The LOWER the U-value is, the better the material is as a heat insulator. (and vise versa)
Payback time:
Payback time (years) = cost of installation / Money saved per year
Specific heat capacity:
-The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C.
E = m × c × θ
