Energy

Solids

• Solids are good conductors of thermal energy because they have a close packed structure and regular arrangement of atoms, which allows them to transfer heat from one atom to another more easily
• Metals are particularly good conductors of thermal energy as they contain free electrons

Conduction Process

• When a metal is heated, the metal ions gain Kinetic Energy (KE) and vibrate more
• This KE is transferred through the metal by free electrons which collide with metal ions and other electrons, thereby passing on the energy

• A shorter rod will conduct more heat than a longer rod because it has less to heat up
• A rod with a larger cross sectional area will conduct more heat as it is wider
• A rod with a larger temperature difference across its ends will conduct more heat

Convection in a liquid (e.g. water in a kettle)

• The element heats up and passes thermal energy to the water nearest to it
• When a liquid is heated, it gains KE and the water molecules start to move faster
• The temperature of the water rises causing the warm water to expand and become less dense
• This warm, less dense water rises to the top of the liquid
• When the hot water at the top of the kettle cools, it becomes less dense and falls back to the bottom of the kettle
• This cycle known as a convection current is repeated until all the water in the kettle has been heated and boils