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A flow of electrons forced into motion by voltage is known as current. The atoms in good conductors such as copper wire have one or more free electrons of the outer ring constantly flying off. Electrons from other nearby atoms fill in the holes. There are billions of electrons moving aimlessly in all directions, all the time in conductors.
When an emf (voltage) is impressed across a conductor it drives these free electrons away from the negative force toward the positive. This action takes place at near the speed of light, 300,000,000 metres per second although individual electrons do not move far they have a shunting effect. This is similar to a number of cars pulled up at traffic lights when the last vehicle fails to stop and hits the second last vehicle which in turn hits the third last vehicle...............
The amount of current in a circuit is measured in amperes (amps). Smaller units used in electronics are milli-amps mA (1 / 1,000th of an ampere) and micro-amps uA (1 / 1,000,000th of an ampere). An ampere is the number of electrons going past a certain point in one second.
The quantity of electrons used in determining an ampere is called "coulomb" which one ampere is one coulomb per second. A coulomb is 6,280,000,000,000,000,000 or 6.28 X 10 18 electrons.
This (a coulomb) is the unit of measuring electrical quantity or charge.
electron theory
voltage
ohms law
resistance
resistor colour code chart
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