A series circuit is one in which items are arranged in a chain, one following the other, so the current has only one path to take. The current is the same through each item.
Series circuits are used for several reasons:
1. To increase a voltage source.
The following is true of any standard battery, but let’s use the AA battery as an example. If you put one AA battery in a circuit, you will have a power source of 1.5 volts because that’s the voltage of a standard AA battery.
If you want 3 volts, you can place two AA batteries in series which gives you 1.5 V + 1.5V, which equals 3V.
Put three AA batteries in series and you will get 4.5 volts, etc.
More coming soon.
Also see: http://physics.bu.edu/py106/notes/Circuits.html