Explain thermal energy
the energy a substance has because of the motion of its microscopic particles. When the thermal energy of a substance increases, its temperature usually does too
Explain conduction
conduction is the transfer of heat (thermal energy) from one place to another through the passing on of kinetic energy between particles. This happens mainly in solids and liquids where particles are closer together. Particles in the hotter region vibrate more energetically and over time, some of this energy is passed along to neighbouring particles, so they also vibrate more. As the process continues through the structure, the temperature rises even in the region furthest from the heat source. In liquids energy is transferred via collisions between the moving particles
Why can’t heat transfer by conduction through a vacuum?
a vacuum doesn’t contain particles
Explain the conduction in different states of matter
solids are best conductors generally as the particles are held close together so transfer of energy is quicker
then liquids
then gases as collisions are not frequent enough
Why are metals good thermal conductors?
In metals in the solid and liquid states, there are free electrons, which can move through the lattice of metal ions. When part of a metal becomes hotter, not only the ions but also the free electrons gain kinetic energy. Ions can only pass on kinetic energy relatively slowly, from one ion to its immediate neighbours and so on. However, free electrons can transfer energy much faster, by moving through the lattice and colliding with ions and with each other. This is why metals are particularly good thermal conductors
Explain the factors impacting the rate of conduction
temperature difference between the two objects (higher gradient leads to quicker conduction)
nature of substance between two objects
distance between objects (shorter distance means less time)
area of object surfaces in contact with connecting material (larger area means quicker conduction)
Explain the effect of temperature on fluid density
as temperature increases, the average speed of particles increases so collisions are more frequent and of greater force. Consequently, the particles move further apart so the fluid expands and becomes less dense
Explain convection
occurs when a region within a fluid is heated by conduction. The warmer fluid becomes less dense than the surrounding so it moves upwards, pushing cooler fluid out of the way and this cooler region moves to take the place of where the warmer fluid was. As the warmer fluid rises, it cold and becomes less dense, and tends to sink. A cycle of moving fluid, called a convection current, can develop in the fluid.
Compare conduction and convection
convection cannot occur in solids
kinetic energy is passed on between individual particles in conduction whereas in convection the heat is transferred by the bulk motion of a group of particles
Explain thermal radiation
Thermal radiation, also called infrared (IR) radiation, is a type of wave that is one of the parts of the electromagnetic spectrum. Like all waves of the electromagnetic spectrum, it travels at the speed of light
and does not need a medium in which to travel. So unlike conduction and convection, thermal radiation can transfer energy through a vacuum. This is how heat is transferred from the Sun to the Earth
Explain the emission of thermal radiation
Any object with a temperature above absolute zero emits thermal radiation. The higher its temperature, the higher the rate at which it emits thermal radiation
What happens if an object is at a higher temperature than its surroundings?
it emits thermal radiation at a higher rate than it absorbs it
All objects both emit and absorb thermal radiation all the time
Explain the factors affecting the rates of emission and absorption of thermal radiation
temperature
surface texture (shiny surfaces cause a lower rate of both emission and absorption)
surface area (smaller surface areas cause a lower rate of both emission and absorption)
What are the 3 methods of transferring heat
conduction
convection
radiation
What is specific heat capacity
the amount of thermal energy needed to increase the temperature of 1 kilogram of a substance by 1 degree Celsius
Specific heat capacity equation
E=mcΔθ
