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.

Hey there!! If 1 Amp is equal to 1 Coulomb, why do we have two separate terms to represent the same idea? Why can’t we just say that current is measured in coulombs? This may be a stupid question, but I would really appreciate if you could shed some light on this. Thank you.

The reason for the confusion here is that 1 Amp DOES NOT equal 1 Coulomb. One Amp is 1 Coulomb PER SECOND. The definition is in fact a bit more complicated, but, the basic from Wikipedia is “The SI unit of charge, the coulomb, “is the quantity of electricity carried in 1 second by a current of 1 ampere”.[11] Conversely, a current of one ampere is one coulomb of charge going past a given point per second: “