Physics Basic Revision Notes - All Resumed
When materials like silk or polythene become charged with static electricity it is because they are poor conductors or insulators and the electrons stay on the surface.
Good conductors like metals allow the electrons to flow away. When the charge builds up it can jump across a gap causing a spark. Static electricity happens in clouds because ice particles rub past each other and build up a charge in the cloud and this charge can jump between clouds or the Earth as lightning.
Electric current is a flow of electrons along a conductor like a metal wire. Electrons come from a source like an electric cell and change places with the metal atom electrons and push the electrons of the metal atoms along the wire. The electric cell gives the electrons energy. Break the circuit and the electrons cannot flow.
Electric current is not used up because electrons are not destroyed they transfer energy as they move round the circuit. This can happen in a resistor or light bulb when thermal energy and light energy are given out. Light bulbs produce light because they have high resistance and resist the flow of the electrons
Series and parallel circuits
In diagram (a) current flows out of the battery through the ammeter and the bulbs, and as the electrons pass through the first bulb some energy is transferred. Then as the electrons pass through the second bulb, more energy is transferred.
The same number of electrons pass along the circuit so the current is the same at all points in the circuit.
In diagram (b) the current flows out of the cell around the circuit and splits between the two bulbs. The current is different in each bulb but the sum of the two currents =...