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| Why does a battery need to be in a circuit loop to work? |
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| IanB:
--- Quote from: roogadget on September 28, 2018, 11:34:28 am ---This is a simple one that I don't get. :P Why can't I connect the positive terminal of one 12V battery to the negative terminal of another 12V battery? Why does it need to be in a loop? --- End quote --- Imagine cars going round and round a race track. They can go round and round forever as long as they have fuel. But if you build a brick wall across the track the cars can only go round it once and then they have to stop because the wall is in the way. It's the same with electricity. If there is no loop to go around it will stop because there is no path to continue. |
| bson:
Think of the chemical energy in a battery as a compressed spring, which exerts a force similar to the electromotive force (electric potential). A compressed spring can't uncompress itself into another compressed spring. A battery "uncompresses" its chemical energy through a flow of charge between its terminals - in effect the near zero conductance of the air between the terminal keeps it charged, and only by closing a circuit between them with a high conductance will you permit it to release its energy. It compresses, or charges, with a current in the opposite direction. Without a conductor to permit a current all you can do is combine potentials - like stacking two compressed springs. |
| Brumby:
There are two issues in your question. The first is current path, which addresses whether a current can flow. The second is potential (pressure) difference, which addresses if it will flow. Using the water analogy - think of each battery as a tank holding water ... and to make the analogy clearer, we will say these tanks are sealed. Now, connect one pipe between the tanks. Will any water flow? Answer: No. The reason why has nothing to do with any pressures involved - just that the water cannot go anywhere. It's only when a second pipe is connected that you have a path for water to be able to flow - and if it flows, it flows around a loop. The second part relates to potential difference - and your implied thinking that the positive on one battery has a potential higher than the negative of the other is quite wrong, unless they are both referenced to (have a connection to) a common point - which they aren't. Without a connection to a common point, every source of electricity (let's exclude electrostatic) is what is called "floating". This is what allows you to stack six 1.5V batteries to get 9V - or two floating power 12V power supplies to give you +/- 12V rails. |
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