You can measure current and potential difference in circuits. They are different things and so are measured in different ways.
Current is measured in amperes. The symbol for ampere is A. For example, 20 A is a bigger current than 5 A. The word ‘ampere’ is often abbreviated to ‘amp’, so people talk about how many amps flow.
A device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but most have a digital display. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.
When two components are connected in series, you can follow the path through both components without lifting your finger or going back over the path you have already taken.
Potential difference is measured in volts. The symbol for volts is V. For example, 230 V is a bigger potential difference than 12 V. Instead of talking about potential difference, people often talk about voltage, so you may hear or see ‘voltage’ instead of ‘potential difference’.
Potential difference is measured using a device called a voltmeter. Just like ammeters, some types have a pointer on a dial, but most have a digital display. However, unlike an ammeter, you must connect the voltmeter in parallel to measure the potential difference across a component in a circuit.
When two components are connected in parallel, you cannot follow the circuit through both components from one side to the other without lifting your finger or going back over the path you have already taken.
You can measure the potential difference across a cell or battery. If the two or more cells point in the same direction, the more cells, the bigger the potential difference.