PHYSICS PAPER 1
P1.1 AQA – ENERGY TRANSFER BY HEATING
Heat radiation is just electromagnetic waves at a certain frequency – Infrared Radiation.
All objects continuously emit and absorb infrared, but an object that is hotter than its surroundings will emit more infrared than it absorbs (whilst it cools down). An object that is hotter than its surroundings will absorb more than it emits, as it warms up.
Dark, matt surfaces are good absorbers and emitters of infrared, whereas shiny, smooth surfaces are both poor emitters and absorbers, but are good reflectors. This is why solar panels are black so they absorb lots of sunlight, but silver blankets keep heat inside.
When a substance is heated, it gains kinetic energy (KE – measures in Joules) making the particles move or vibrate faster. Temperature (°C) is a measure of the average kinetic energy in an area.
Energy travels from hot objects to cold areas and the greater the difference, the faster the rate of change.
In solids, strong forces of attraction hold particles together in a fixed, regular arrangement. The particles have little energy, and so can only vibrate about fixed positions.
In liquids there are weaker forces of attraction between the particles that are close, but can move past each other to form irregular arrangements. They have more energy than particles in a solid and can flow past each other in random directions at slow speeds.
In gases there are almost no forces of attraction so the particles are free to move and have more energy than in both liquids and gases – they move in random directions at high speed.
When a substance is heated it gains kinetic energy, so the particles vibrate faster until a change of state occurs – solids may melt or liquids start to boil.
Solids conduct energy as their particles are close together in regular patterns, but since the particles in gases and liquids can move about, energy is transferred by convection.
Conduction is the process where vibrating particles pass on kinetic energy to neighbouring particles.
Metals are particularly good conductors, as the electrons are free to move within the metal, which is a faster way to pass on the energy than in non-metals (why non-metals are used as insulators)
Convection occurs when the more energetic particles move from the hotter region to the colder region and take their heat with them.
Condensation is when a gas turns to a liquid when the particles in a gas cool and slow down enough to lose kinetic energy and be pulled together into a liquid. Water vapour in the air condenses when it comes into contact with cold surfaces.
Evaporation is when a liquid turns into a gas, and particles can evaporate from a liquid at temperatures much lower than its boiling point. Particles near the surface of a liquid can escape if they are travelling in the right direction to escape, and if they are moving fast enough to…