Energy Conservation in Parallel Circuits


So each “closed loop” experiences the same voltage drop as the emf of the cell. So if you added the “total” voltage drop in the circuit, it would exceed that provided by the cell.

Voltage is Joules per Coulomb.

The number of Coulombs in a circuit is fixed.

Maybe it is the product of Voltage and Current which is conserved in parallel circuits? I’m struggling to work it all out in my head probably because I’m not sure what the basic rules of circuits are and how they relate to Physics I’ve encountered elsewhere. It all just seems a little bizarre and contradictory.

(UK A-Level)

In: Physics

3 Answers

Anonymous 0 Comments

There are major flaws in your intuition.

If you are at A level, I assume you know that work done = force x distance.

Imagine you have a road between your house and school that is 1km long. One day you decide that a new road is needed and you build a second road parallel to the existing road. Since now you have 2 roads each 1km long, could you say you’ve violated energy conservation because now you have a total of 2km of road rather than 1?

Say you have a sibling that both travel to school. And rather than each of you taking the same road, one of you use the old road and the other the new road. Did you double the amount of work needed in total for the both of you to get to school once each of you took a different road? (assume that the force needed per person is the same)

Using your own analogy, if you have a fixed number of coulombs but had 2 paths, you’d divide the coulombs across the 2 paths. So the total energy content remains the same since it (in total) it is the same number of coulombs travelling across the same voltage, they just took different paths. [this is a very bad analogy for future intuition, by the way]

A more commonly used analogy (that gives a better intuition) is to think of your circuit as water pipes, voltage is the pressure difference and current is the flow rate of the water in the circuit.

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