Series circuits have only one pathway for the electric current to flow through.
Components are connected in a line to form a series circuit
If one component is disconnected or removed, then the whole circuit will stop working. This isn't great
The more cells in a circuit = the more potential difference there will be
The total potential difference is shared across all components, this adds up to the source potential difference.
V total = V1 + V2 +...
Ammeters are connected in series
The current is always the same in all components
I 1 = I 2 =...
The current depends on the total potential difference and total resistance
I = V/R
The total resistance is the sum of all the components' resistances.
R total = R1 + R2 +...
By adding a resistor in series means that the two resistors have to share the total potential difference.
The potential difference between each resistor is lower, so the current across it is lower (directly proportional). Current is the same everywhere in a series circuit, so the total current decreases when a resistor is added. This means that the total resistance increases
Current and potential difference are directly proportional, so when one increases the other increases :)
Current is inverselyproportional to the resistance. So when the current decreases the resistance increases :)
The more resistance a component has, the bigger share of the total potential difference (less potential difference can flow through the component)
For the diagram here, calculate the current passing through the circuit: