P1aL3 Conduction and Convection

Key Words

Conduction - movement of heat energy through solid materials

Conductor - a material that transfers heat energy easily.  Also called thermal conductor.

Convection - transfer process of energy in liquids and gases.

Expand - materials occupy more space as they get hotter.

Heat energy - energy flowing from a hot object to a cold object.

Insulator - material that transfers heat energy badly.  Also called thermal insulator.

Particle Model - explaining conduction and convection in the way that molecules behave.

Transmit - passing energy on from molecule to molecule

Vibrate - To move in a forwards and backwards  (or up and down) movement

Grade E

Conductors pass heat energy easily, e.g. metals.  Heat does not flow well through insulators.  Therefore bad conductors are good insulators.

In convection, hot liquid (or gas) expands and becomes less dense ("lighter").  It rises to the top of the liquid, pass in the heat to the cooler areas.  As it cools it gets denser and falls back to the bottom.  You can see peas in a pan moving up and down on the convection currents.

Liquids are poor conductors of heat; gases are even worse.

Grade C

In the particle model, the hot material vibrates more and bumps into neighbouring molecules.  The heat in the form of increased vibration is passed on from one molecule to another.

With increased vibration, the space occupied by the material increases.  The material expands.

When the material expands, the same amount of material (mass) stays the same, so the material gets less dense.

Uses:

• Pans are made of metals like copper, which is a good conductor.  The handles are made of wood, a good insulator.
• Air trapped in the fibres of your duvet cannot move by convection, so act as a good insulator.
• Fans blow cool air over hot components like the CPU in your computer.  This is called forced convection.

Metals conduct well because they have free electrons that are not bound to atoms.  They can transfer heat even more quickly than vibrating molecules.  The movement of of the electrons is an electric current (which is why metals conduct electricity well).

Insulators do not have free electrons.  They don't conduct heat well, and don't conduct electricity either.

Grade A

Water is a good coolant because the specific heat capacity is high.  This means that a small amount of water can hold a lot of heat for a relatively small temperature rise.

Diamond conducts heat very well, but does not have free electrons.  The carbon atoms are bound in a very tight structure, whcih enables it to transfer vibrations well, as well as making it chemically unreactive and very hard.