Lesson 2 notes – Conduction
Objectives
Describe what thermal energy is.
Explain conduction as the movement of heat energy through vibration of particles and
movement of free electrons.
Be able to describe an experiment to compare conducting materials.
Heat
All objects are made up of particles. These particles are vibrating about all the time
unless they are at absolute zero (-273 degrees Celsius). The vibration of these
particles in an object is known as thermal energy. If the particles vibrate more or there
are more vibrating particles there will be more thermal energy.
If we compare the thermal energy in a bath to that of a cup of tea at the same
temperature, the bath would have more thermal energy because there are more
particles.
Solid Liquid Gas
In a solid, particles vibrate about fixed positions.
As they gain more energy the bonds break and the particles can
move between one another.
If more thermal energy in given to the material the liquid turns into a
gas, the particles have enough energy to move freely to fill the
volume that they are in.
Conduction
Conduction is the transfer of energy between particles. Particles in solids that have
particles closely packed together will transfer energy easier as it is easier for the
particles to collide with each other. As one particle is given energy and starts to
vibrate, the bonds that hold it to the particles around it will also begin to vibrate and so
transfer the thermal energy on.
Bad conductors
Bad conductors are called insulators. The particles in
insulators are spread out and so don’t pass on the
energy very well. Fluids also are bad conductors as
particles can flow between each other.
The picture shows a typical demonstration where the
water at the top of the boiling tube is heated to boiling
point whilst the ice at the bottom of the tube remains. This happens because water is a
poor conductor of heat.
Gases that have particles that are very spread out are the best insulators and pockets
of air are specifically put into many materials to make them better insulators (lesson 4).
Conducting bars
An experiment to compare the conduction through different materials is described below:
Which material conducts the heat along it the fastest?
Method
A drawing pin is placed on the end of different materials with Vaseline.
The materials are put on the top of a tripod and the ends are heated with a Bunsen
burner.
The time is taken until each of the pins falls off.
The faster the time, the better the conductor.
Conduction in metals
As well as vibration of particles, metals also have free electrons that can move around
inside in between each of the particles. So metals that have lots of free electrons, like
copper, are very good conductors of heat (as well as electricity).
Heat Transferred