2.1.7

Heat Energy Transfer

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Conduction

Heat energy can move through a solid by conduction. We can show this in 2 ways:

Water

Water

  • An ice cube is at one end of a test tube and water is at the other end of a test tube.
  • We can boil the water at one end without the ice cube melting.
  • This shows that water is a poor conductor of heat energy.
  • We say that water is a bad thermal conductor.
Metal rods

Metal rods

  • Different metals conduct heat energy at different rates.
  • We place metals in boiling water at one end and put wax on the other end.
  • The wax that melts fastest will be attached to the metal that is the best thermal conductor.
  • Copper is a better thermal conductor than aluminium and iron.

How Conduction Happens

There are two mechanisms for conduction in a solid.

Lattice vibrations

Lattice vibrations

  • If one part of a solid is heated, the particles in that part gain energy and vibrate more.
  • These vibrations then transfer heat energy to neighboring particles which also vibrate more.
  • The closer particles are together (in a denser solid), the better the solid will conduct heat energy.
Electron transfer

Electron transfer

  • Metal lattices contain free (delocalized) electrons that can move anywhere in the lattice.
  • These electrons gain heat energy in the hot part of the object and carry it to other parts of the lattice.
  • Solids with more free electrons are better thermal conductors.

Convection

Liquids and gases are called fluids because they can flow. They do not conduct heat well, but they can transfer heat energy using convection currents. Convection currents are created by areas of different densities in a fluid. They work like this:

Stage 1

Stage 1

  • When part of a fluid is heated, the particles in this area gain kinetic energy.
  • When the particles gain kinetic energy they move away from each other, so the area that has been heated becomes less dense and the warm fluid particles rise.
Stage 2

Stage 2

  • When the particles in the warm part of the fluid rise they transfer some of their energy particles to in the cold fluid nearby.
  • The heated particles then begin to sink because their density increases.
Stage 3

Stage 3

  • At the bottom, colder fluid particles that haven't been heated will replace the warm particles that have risen.
  • These colder particles are then heated. They move apart and start to rise.
Stage 4

Stage 4

  • This cycle creates convection currents. Convection currents are the result of different densities in the fluid. These different densities are created by heating.
Jump to other topics
1

Space, Time & Motion

2

The Particulate Nature of Matter

3

Wave Behaviour

4

Fields

4.1

Circular Motion

4.2

Newton's Law of Gravitation

4.3

Fields

4.4

Fields at Work

4.5

Electric Fields

4.6

Magnetic Effect of Electric Currents

4.7

Heating Effect of Currents

4.8

Electromagnetic Induction

4.9

Power Generation & Transmission

4.10

Capacitance

5

Nuclear & Quantum Physics

6

Measurements

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