Charge and current
Posted in Physics, SensingWhen you switch on a light it lights up seemingly instantly however the electrons do not move very fast, they have been there all along in the metal of the wire and filament of the bulb.
An electric current is the net movement of charged particles in a certain direction. Think of it as a tube full of marbles. When you put another marble in the tube one falls out almost instantly the other end, the marbles in the tube however haven't moved that much.
Charge
Charge is measured in coulombs (C) with a single electron carrying -1.6 x 10-19C of charge. Therefore the amount of electrons needed to carry 1C of charge can be calculated:
The amount of charge is therefore the number particles multiplied by the charge of each particle:
Current
Current is the rate of flow of charge and is measured in amperes which is often shortened to just amps. 1 ampere of current is equal to 1C of charge flowing past a point in 1 second, hence:
Current-time graphs
Charge is equal to the area under a current (I) vs time (t) graph.
Measuring current
In order to measure current as accurately as possible ammeters should have as little resistance as possible to be sure not to change the current it is trying to measure.
Series and parallel circuits
In a series circuit the current is the same everywhere. In a parallel circuit however the current is split between each branch of the circuit.