Current

In a parallel circuit, current will be different in each branch. The total current of the circuit (the current coming out of the power source) will be equal to the sum of the current in each branch. This means that current coming out of the power source will equal the sum of the current running through the 220-ohm resistor branch and the 330-ohm resistor branch.

Let's look at this with Ohm's law to see how this works. To calculate current with Ohm's law we use the formula I=V/R, which means the current equals the voltage divided by the resistance. Earlier, in the resistance section, we calculated that the resistance in the circuit was 132 ohms and we know that the voltage is 9 volts, therefore, the total current will equal 9 volts/132 ohms or 0.0682 amps (68.2 milliamps).

We can also use Ohm's law to calculate the current in each branch knowing that the voltage for each branch will be the same 9 volts. The current in the branch that contains the 220-ohm resistor would be 9 volts/220 ohms or 0.0409 amps (40.9 milliamps). The current in the branch with the 330-ohm resistor would be 9 volts/330 ohms or 0.0273 amps (27.3 milliamps).

We can now add the current from the branch that contains the 220-ohm resistor to the current from the branch that contains the 330-ohm resistor to get the total current of 40.9 milliamps + 27.3 milliamps, which equals the same 68.2 milliamps coming out of the power source.

Now that we understand the difference between parallel and series circuits, there is one more concept we need to understand before we can get started building things. This concept is a voltage drop.