Physics - Energy transfer through heating

conduction

transfer of heat through direct contact in solids

thermal conductivity

the rate at which a substance transfers heat

Convection

The transfer of thermal energy by the circulation or movement of a liquid or gas

How conduction works

As one end of a solid object is heated, energy is transferred to the kinetic energy stores of the particles in that end.

This causes the particles to vibrate faster, and so they collide with their neighbouring particles more often.

As the collisions transfer kinetic energy, their neighbours also vibrate faster and collide more often with their neighbours.

This process repeats over and over again so that energy is effectively passed along the object from one particle to the next.

Even though it's kinetic energy that's being passed between particles, when considering the object as a whole we say that it's heat (or thermal energy) that's being transferred.

How convection works

As a fluid is heated the particles gain kinetic energy and expands

This causes the fluid to become less dense and so it will rise above any cooler fluid that hasn't been heated (because that fluid is more dense).

As the fluid cools down it will become more dense again, and so sink back down.

If this process takes place in a limited space, like a container or a room, it can create a convection current.

Thermal Radiation

The transfer of heat through infrared waves

Constant temperature

An object at a constant temperature emits and absorbs infrared radiation at the same rate.

High temperature

The higher the temperature of an object, the more infrared radiation it emits in a given time

black body

a perfect emitter and absorber of all wavelengths of radiation

Hotter objects ...

emit colors with shorter wavelengths

Greenhouse effect

when gases (such as water vapour, ethane and carbon dioxide) absorb infrared and emit it back to the earth's surface. This process makes the earth warmer

specific heat capacity

The energy required to raise the temperature of one kilogram of a substance by one degree Celsius

A material with a higher specific heat capacity takes more energy to heat 1kg by 1 degree Celsius

Specific heat capacity formula

Energy = mass × specific heat capacity × change in temperature

Higher specific heat capacity

A substance with a high specific heat capacity absorbs and stores heat well

lower specific heat capacity

a substance with a low specific heat capacity heats up and cools down quickly.

Do metals have a high or low specific heat capacity?

low specific heat capacity