Simple Circuits

When there is only one path for current to follow, elements are connected in series. Adding additional elements in series increases the length of the circuit; thus, increasing the total resistance of the circuit. If the voltage of the power source is kept constant, adding elements in series will decrease the circuit current. The equivalent resistance for series elements is found by adding the individual resistances. 

When there are multiple paths for current to follow, elements are connected in parallel. Adding additional elements in parallel increases cross sectional area; thus, decreasing total circuit resistance. If the voltage of the power source is kept constant, adding elements in parallel will increase the circuit current. The equivalent resistance for parallel resistors is found by adding 1/R for each individual resistance, then taking the reciprocal of that sum. We will use these relationships to analyze combination circuits in the next topic.