Heat Radiation, Electricity and Waves

Infrared radiation 

• All objects emit and absorb infrared radiation
• The hotter an object is the more infrared radiation it raduates
• Dark, matt surfaces are good abosorbers and good emitters of infrared radiation 
• Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation
• Light, shiny surfaces are good reflectors of infrared radiation 

Vacuum flasks 

• The glass bottle is double walled with a vacuum between the two walls. This stops all conduction and convection through the sides
• The walls either side of the vaccum are silvered to keep heat loss by radiation to a minimum 
• The bottle is supported using insulating foam. The minimises heat conduction to or from the outer glass bottle
• The stopper is made of plastic and filled with cork or foam to reduce any heat conduction through it 

Kinetic theory 

• This theory explains the different states of matter and the particles of solids, liquids and gases have different amounts of energy
• Solids - have a strong force of attraction helds the particles close together in a fixed regular arrangement. Particles do not have much energy so they can only vibrate about a fixed position
• Liquids - there is a weaker force of attraction between particles, which are close together but can move past each other to form irregular arrangements. They have more energy than solids so can move in random directions at low speeds
• Gases - Almost no forceof attraction between particles. The particles have more energy than liquid and soilds. So they are free to move and travel in random direction at high speeds

Conduction 

• Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbourings particles 
• Metals are good conductors due to their free electrons 
• Conduction is more efficient through a short, fat rod than through a long, thin rod. It all comes down to how far the electrons have to transfer the energy.

Convection

• Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them 
• Convection currents are all about change in density.

Condensation

• When gas cools the particles lose kinetic energy and the attractive forces between particles pull them close together
• If the particles get cold enough and the particles get close enough together then condnsation takes place. 
• Water vapour in the air condenses when it comes into contact with cold surfaces
• The rate of condensation will be faster if the:

Temperature of gas is lower
Temperature of the surface the gas touches is lower
Density is higher
Airflow is less

Evaporation

• This process is when particles escape a liquid.
• Particles near the surfaces escape and become gas by:

travelling in the right direction to  escape the liquid

particles are travelling fast enough to overcome thier forces of attractive forces of the others

• When particles escape this decreaese the average energy of the particles so temperature of liquid decreases
• The rate of evaporation can be faster:

Temperature is higher
Density…