Ohm's Law

Ohm's Law states "At constant temperature, the ratio of the potential difference across a resistor to the current flowing in the resistor is a constant."

This, simply stated, means that you can find the value of a resistor by dividing the potential difference (voltage) across the resistor by the current flowing through the resistor. R=V/I or V=IR

Series Circuits:                           

In a series circuit there is only one path that the current may follow. Therefore the current is the uniform in all components of the circuit.

By knowing any two out of the three properties (voltage, current, and resistance), you can get the  third, by Ohm's Law. Remember though, that you need the total of each property though (ie. total voltage, total current or total resistance). To get these total in a series circuit you have to

- Add all the batteries (if more than one) together. This gives you V_total

- Add all the resistors together. This gives you R_total

- For I_total, only one current measurement is necessary because the current is uniform. Also remember V=IR so V_total/R_total=I_total. Therefore you may not even need to do any calculations.

You would use a series circuit if you need a lot of power to operate something. For example many portable stereos require you to place batteries in series.

Parallel Circuits:

In a parallel circuit there is more than one path that the current can follow. Therefore the voltage is uniform across the circuit.

Again, you only need two of the three properties to use determine the third by Ohm's Law. To get the total values in this kind of circuit you need to

- add the currents through each branch of the circuit together. This gives you I_total.

- 1 over the sum of the reciprocals of the resistances will give you R_total.

- for V_total, if not given, only one measurement needs to be taken because the voltage is uniform    across the circuit.

You would use a parallel circuit if you wanted something to last a long time. Remote control and programmable calculators often require batteries to be placed in parallel.