There are two types of electrical circuit: series and parallel.
In series circuits, the components are connected in one loop. The current that flows through all the components is the same. The diagram below shows a series circuit, where two bulbs are connected in series. If one breaks, the other one will not light, because there is only one loop.
When there is more than one loop in the circuit, the components are connected in parallel. The diagram below shows two bulbs connected in a parallel circuit. If one breaks, the other one will still work, because there are two loops, so the current flowing through them is split in two. Christmas tree lights are connected in parallel, so if one breaks, the others can still be used.
Ammeters measure current in amperes or amps (A). Ammeters are always connected in series. Voltmeters measure voltage, which is the potential difference (difference in electrical energy) and drives the current flow. Voltage is measured in volts (V). A voltmeter is always connected to a circuit in parallel to the component with the voltage to be measured.
Current in a series circuit is the same everywhere, so the ammeter will show the same reading anywhere you connect it. If you add more cells, the current will increase. In a parallel circuit the current splits between the different branches.
It is important that you familiarise yourself with these electrical symbols:
Now we will go through some questions on series and parallel circuits.