A series circuit is one where all the components (batteries, bulbs, motors, resistors, ammeters etc.) are all connected one after the other. Such a circuit is shown in Figure 1.
There are
some important properties of series circuits:
(a) the circuit will only work if there is a
continuous loop with no break in the circuit
(b) the current in every component in the
circuit is the same
(c) the reading on an ammeter would be the same wherever it is
placed in the circuit
(d) if you were to add up the voltages (potential differences) across
all the components in the circuit you would get the voltage of the energy source in that circuit
(battery or generator)
(e) no current 'gets lost' as it flows round the circuit – it is only the
energy of the current that gets less as it is converted to other forms of energy such as heat,
light and sound as it passes through each component
You can understand something more about the series circuits by looking at the two parts of Figure 2. Figure 2(a) is a series circuit with two bulbs, two ammeters and a cell. The reading on each ammeter will be the same showing that the current is the same at all points round the circuit – no current is 'lost'. The same number of electrons flow past any point in the circuit every second - no electrons are lost. Although the number of electrons is always the same their energy gets less as they move round the circuit. This energy appears as heat, light or magnetism.
You can
compare this with the runners in a steeplechase shown in Figure 2(b). They "lose" most of
their energy over the jumps just as the electrons transfer most energy when they pass
through a resistor, bulb or loudspeaker. The electrons cannot 'give up' as they move round
the circuit. The energy lost in the connecting wires is negligible and we are going to assume
that the runners loose hardly energy on the flat parts of the steeplechase.
The
energy lost and therefore the voltage difference across a component depends on the resistance
of the component – bigger resistance means a bigger energy loss. In the same way a higher
barrier means a greater energy loss for the runners.