The Series Circuit
A series circuit has more than one resistor (anything that uses electricity to do work) and gets its name from only having one path for the charges to move along. Charges must move in "series" first going to one resistor then the next. If one of the items in the circuit is broken then no charge will move through the circuit because there is only one path. There is no alternative route. Old style electric holiday lights were often wired in series. If one bulb burned out, the whole string of lights went off.
Below is an animation of a series circuit where electrical energy is shown as gravitational potential energy (GPE). The greater the change in height, the more energy is used or the more work is done.
In this animation you should notice the following things:
- The battery or source is represented by an escalator which raises charges to a higher level of energy.
- As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy.
- The charges do more work (give up more electrical energy) as they pass through the larger resistor.
- By the time each charge makes it back to the battery, it has lost all the energy given to it by the battery.
- The total of the potential drops ( - potential difference) across the resistors is the same as the potential rise ( + potential difference) across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery.
- The charges are positive so this is a representation of Conventional Current (the apparent flow of positive charges)
- The charges are only flowing in one direction so this
would be considered direct current ( DC ).
The following rules apply to a series circuit:
- The sum of the potential drops equals the potential rise
of the source.
- The current is the same everywhere in the series circuit.
- The total resistance of the circuit (also called effective
resistance) is equal to the sum of the individual resistances.
Ohm's Law may be used
in a series circuit as long as you remember that you can use the formula
with either partial values or with total values but you can not mix
parts and totals.