Electricity is the flow of electrons from one atom to another. When we talk about current with regards to electricity, we are referring to the amount of electrons flowing past a single point in a circuit. Imagine it like measuring how drops of water are flowing past you in a river.
You might want to learn a little about what electricity is first before proceeding, we covered that here.
Because electrons are so small, vast numbers of them can flow through even the smallest circuit. Just like a vast number of water droplets can flow past you in a small stream.
To be able to quantify the flow of electrons in a circuit, scientist derived some units of measurement to group millions and millions of electrons together. As much as it wouldn’t be practical to measure the flow of drops in a river, it isn’t practice to measure the flow of electrons in a circuit. So units of measurement were created to measure this.
The SI unit of measurement for current is known as the Ampere, or Amp for short. The symbol A is used to represent this value. See Figure 1 below.
This is an Amp reading from an ACB. It reads that on cable 1, there are 346Amps flowing at that specific moment in time. That’s a lot of electrons! I’ll explain why below.
So I mentioned that electron are grouped together, these groups are called Coulombs. How many electrons are in a Coulomb?
1 Coulomb = ~6,242,000,000,000,000,000 electrons! (6.242*10^18)
1 Amp = 1 Coulomb
So in the example where 346Amps were flowing in that cable, how many electrons were flowing?
346A = 346 Coulombs
346*6.242*10^18 = 2.16*10^21
or 2,162,500,000,000,000,000,000 Electrons. Now do you see why we use the unit of Amps.
You may also come across a current rating in mA which is known as a milliampere or milliamp for short. A milliamp is one one-thousandth of an ampere.