P2: Energy transfer by heating

Conduction Convection Radiation

Good thermal conductors Good conductors of electricity

Conduction occurs mainly in solids It is the process where vibrating particles transfer energy to neighbouring particles

Energy transferred to an object by heating is transferred to the thermal store of that object. This energy is then shared across the kinetic energy stores of the particles of the object

Particles in part of an object being heated, vibrate more and collide with each other. The collisions cause energy to be transferred between kinetic energy stores.

Thermal conductivity is a measure of how quickly energy is transferred through a material in this way. Materials with a high thermal conductivity transfer energy between particles quickly

Convection occurs only in liquids and solids. Convection is when energetic particles move from hotter to colder regions

Particles move faster and space between individual particles increase. This causes the density of the heated region to decrease. Because gases and liquids can flow, the warmer and less dense region will rise above colder, denser regions. if there is a constant heat source, a convection current is creeated.

Radiation creates convection currents and only occurs in gases. Heating a room with a radiator relies on creating convection currents in the air of the room. Energy is transferred from the radiator to the nearby air particles by conduction. The air by the radiator becomes warmer and less dense. The warm air rises and is replaced with cooler air. Cooler air is then heated by the radiator. At the same time, previously heated air transfers energy to the surroundings (walls and contents of the room). It cools, becomes denser then sinks. The cycle repeats causing a flow of air to circulate around the room. This is a convection current.

Lubrication Insulation

Reduces frictional forces. When something moves, theres normally at least one frictional force acting against it. This lets some energy in the system dissipate. Eg: Air resistance can transfer energy from a failing object’s kinetic energy store to its thermal energy store. Objects being rubbed together, lubricants can reduce the friction between the object’s surfaces when they move. Lubricants are usually liquids (eg: oil) so they can flow easily between objects and coat them

Insulation is material designed to prevent heat or sound from being transmitted from one area to another

Thick walls Double glazed windows Draught excluders Loft insulation Cavity walls

Have thick walls made from a material with a low thermal conductivity. The thicker the walls and the lower the thermal conductivity, the slower the rate of energy transfer will be so the building will cool slowly

Draught excluders are located around doors and windows, and reduce energy transfer by convection

Cavity walls are made up of an inner and outer wall with an air gap in the middle. Air gaps reduce the amount of energy transferred by conduction via walls. Cavity wall insulation with a foam air gap also reduces energy transfers by convection in our wall cavity Double glazed windows work the exact same way

Loft insulation can be laid out across the loft floor and ceiling. Fibreglass wool is often used which is a good insulator as it has pockets of trapped air. Loft insulation reduces energy loss by conduction and prevents convection currents from being created