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Series and parallel circuits

In a series circuit (Figure 1(a) the current at any point is the same. However this is not true in a circuit containing two or more components where there is a branch. Such a circuit is called a parallel circuit; the components in the circuit are parallel with each other (Figure 1(b)).

Although the current in one branch may be more than the other the potential difference between the two ends of the branch will be the same no matter through which branch you measure it. Therefore the loss of energy of each coulomb as it passes from one end of either branch to the other will be the same. You can compare this with the gravitational energy lost by going down to the ground floor of a building by the lift or the stairs the gravitational potential energy lost in each case us the same. It depends only on the height change (and mg of course).

As long as the supply voltage does not alter, changing the current in one branch of the circuit has no effect on the current in the other. Compare this with a bath where water is running out of one plughole (Figure 2).

Making another hole in the bottom of the bath will not affect the volume/sec of water running from the first plughole. It will only alter the total water flow. The pump will have to work harder to keep the level of water in the bath constant.

© Keith Gibbs 2011