The Parallel Circuit


A parallel circuit has more than one resistor (anything that uses electricity to do work) and gets its name from having multiple (parallel) paths to move along . Charges can move through any of several paths. If one of the items in the circuit is broken then no charge will move through that path, but other paths will continue to have charges flow through them. Parallel circuits are found in most household electrical wiring. This is done so that lights don't stop working just because you turned your TV off.

Below is an animation of a parallel 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 following rules apply to a parallel circuit:

  1. The potential drops of each branch equals the potential rise of the source.
  2. The total current is equal to the sum of the currents in the branches.
  3. The inverse of the total resistance of the circuit (also called effective resistance) is equal to the sum of the inverses of the individual resistances.


    One important thing to notice from this last equation is that the more branches you add to a parallel circuit (the more things you plug in) the lower the total resistance becomes. Remember that as the total resistance decreases, the total current increases. So, the more things you plug in, the more current has to flow through the wiring in the wall. That's why plugging too many things in to one electrical outlet can create a real fire hazard.

 

Ohm's Law may be used in a parallel 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.


1998 Science Joy Wagon