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# batteries in parallel Watch

1. In terms of energy gain and lost by a 1C charge; Why is it that when two 6V batteries are connected in parallel , they give an e.m.f. of 6V?
2. The emf of a supply is the amount of energy transferred by it to a unit charge. A standard model that works well is to think of this energy being given to the charge when it passes through the supply.

If we have just one battery, a coulomb of charge has to pass through this battery. So, if it's a 6 V battery, it transfers 6 J to the coulomb of charge.

Now consider two 6 V batteries in parallel. Along comes a coulomb of charge to pass through the combination. Some of it (let's say exactly half for the sake of convenience) passes through one batter, the rest through the other. So, 1/2 of the coulomb is given energy by one battery. How much? W = EQ tells us that this half of the coulomb is given 6 x 1/2 = 3 J of energy. Similarly, the other half of the coulomb is given 3 J of energy. So in total, the entire coulomb has been given 6 J of energy. The parallel combination has delivered 6 J of energy to one coulomb of charge, and can therefore be considered as a single supply of emf 6 V.

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Updated: April 10, 2013
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