aka...science room
light switch
Light switches, what would we do without them? Probably blunder about aimlessly in the dark.
But a simple flick of a switch allows electric current to move around a circuit and through the filament wire of a light bulb. The wire heats up rapidly and gives off light, illuminating your way.
An electric current is the flow of negatively charged particles called electrons. But electrons will only move if there is a potential difference between each end of the circuit.
The potential difference is produced by the battery which has a positive end (lack of electrons) and a negative end (excess of electrons). This imbalance of electric charge also means that the battery creates an uneven electric field.
Once a circuit is complete, electrons will move towards the positive end of the battery.
Once on the move, electrons don’t actually travel very fast. The average speed of an electron through a copper wire is just 0.01 cm/s. Each individual electron has a tortuous journey through the wire as it continually bangs into the atoms that make up the wire.
So how come the light turns on as soon as you flick the light switch? Electric fields travel at the speed of light so when the switch is closed, the electric field produced by the battery very quickly passes the message to all the electrons in the wire that they ought to start moving.
This means there is only a tiny, and unnoticeable, time delay between flicking the switch and the light turning on.
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