Can you define current, potential difference and resistance in a circuit, and give their units?

Current is the flow of charge in the circuit, a bit like the flow of water in a river, and is measured in Amps (A).

Potential difference is defined as the 'work done per unit charge', which is related to the voltage across (and so the energy supplied to) a component in the circuit. It's measured in Volts, (V).

Resistance is the quantity that describes how difficult it is for a current to flow in a circuit (think of traffic trying to get through a narrow tunnel vs a motorway), and is measured in Ohms, (Ω).

Bonus: do you know the relation between these three quantities? 

A: it's called Ohm's law, and it states that R=V/I, or resistance is potential difference divided by current.

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