Lessons · Electrical · what electricity is
What is actually moving in the wire
Electricity is charge on the move. Current (amps) is how much charge passes each second, voltage (volts) is the push that moves it, and resistance (ohms) is how hard the path makes that push work.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
First week on a job, a foreman says 'that circuit is pulling twenty amps' and 'we have got 480 on that bus'. If amps and volts are two words for the same thing to you, every instruction after that is noise. The three words are three different things, and every reading on a meter is one of them.
How to think about it
Picture water in a hose. Current is the flow, voltage is the pressure, resistance is how narrow the hose is. Then attach the unit to every number you say or write: 20 A, 120 V, 6 Ω. A number with no unit is a guess.
Worked example
I = 20 ATwenty amps of current. A count of charge going past one point in the wire each second.
V = 120 VOne hundred and twenty volts. The push between the two wires; it is there whether or not anything is drawing current.
R = 6 ΩSix ohms of resistance. The load's own property, the same whether the circuit is on or off.
250 mA = 0.25 AMilli means a thousandth. Small currents come in milliamps; convert them to amps before you calculate.
Your turn
Write 1.8 kW in plain watts.
1.8 kW = W
Solve one, graded on the server
The trap
Saying a wall outlet 'has' 15 amps. The outlet has 120 volts waiting; the amps only exist once something is plugged in and drawing them, and how many depends entirely on that something.