2.9 understand that the current in a series circuit depends on the applied voltage and the number and nature of other components

Current:

Current in a series circuit is worked out using the formula:

Current = Voltage ÷ Resistance

Current is measure in Amps
Voltage is measured in Volts
Resistance is measured in Ohms

If there are more components, there is more resistance

If there is a higher voltage, the current will be higher