P1aL10 Electricity and Heat

Key Words

Component - a part in an electrical circuit

Electrical Appliance - a device that terns electricity into useful energy

Electrical current - how many electrons flow in one second

Electrical Energy - transfer of energy by movement of electrons.

Filament - a very thin wire that glows white hot in a light bulb.

Fuse - a weak link made of thin wire that melts when too big a current flows through it.  It protects the appliance if there is a fault.

Heat energy - transfer of energy from hot objects to cold objects.

Resistance - the amount by which a conductor opposes the flow of current.

Test Yourself

Homework
Physics GCSE
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Grade E

Many appliances get warm when they have been on for a while.  When electrical currents flow through an appliance, most of the electrical energy is turned into useful energy.  However some is wasted as heat.

Of course we can use the heating effect of a current:

  • In a hotplate, thin resistance wire gets hot and the heat is transferred to the pan;
  • In a bulb the filament glows white hot.
  • Fuses melt if too big a current flows through them, protecting the appliance from further damage if there is a fault.

When an appliance keeps on blowing its fuse, some (thick) people replace the fuse with thicker wire, or even nails.  This is asking for trouble, which will come in the form of the appliance going up in flames.

Grade C

Thin wires have a high resistance.  Resistance occurs when the electrons that form the current bump into the metal atoms.  The collisions make the atoms vibrate more and the wire gets hot.

Metals are all good conductors, but some are better than others.  Copper is a far better conductor than steel, although it is much more expensive.  It is used in wires as it will stay cool even if it's carrying a big current.

The bigger the current is, the thicker the wire has to be.

Note the thick wires leading to the traction motor for an electric locomotive.

Grade A

Some materials lose almost all their resistance when very cold (about -270 oC).  They are called super-conductors.  Very little energy is lost as heat.

There is research into high temperature super-conductivity, but the temperatures are still -150 oC, which is still very cold, and needs a lot of energy to achieve.