Why doesn’t current flow when I connect the positive pole of one battery to the negative pole of another? In the moment of contact, shouldn’t the electrons that are abundant in the negative pole want to rush to the positively charged pole of the other battery until the charge in both poles equalizes?
My mental model of a battery is a water tank that has a wall through the middle, giving it two partitions. One of them is full of water, the other empty. Now you can connect a hose from one end to the other and water will flow from full to empty until the water level equalizes. But if you connected the empty side of one tank to the full side of another tank, water would still flow. Clearly my model is flawed. Can someone explain? Thank you!
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Equating water to electricity is an analog that breaks down when looked too closely at.
Batteries don’t actually store electrons that’s what capacitors do. Batteries are more like pumps that exploit a chemical reaction to ‘push’ electrons to one side of them.
However when electrons aren’t being returned to the other the chemical reaction stops because there’s nothing left to push (or rather the positive charge that builds up due to lack of electrons attracts the remaining electrons more then the chemical reaction can push against).
Two batteries connected positive to negative don’t form a circuit. You need a circuit for electricity to flow. That means in addition to the connection between batteries that you mention, you have to connect their other poles to form a circuit.
Your example with the water is fatally flawed simply because water flows according to gravity, electricity flows according to the orientation of the poles on the batteries and the presence of a circuit to flow through.
Two batteries is not a circuit. It’s a component in a circuit. You have to add more to it before energy will flow.
Batteries release electrons through a chemical reaction. That chemical reaction can only take place when you complete the circuit. I.e connect the battery’s positive to it’s own negative.
Connecting the positive of one battery to the negative of another does not complete the circuit for either batteries, so the chemical reaction does not proceed and thus no electron flow/no current.
A microscopic amount t of current does flow, but it’s quickly stopped by the charge imbalance in the battery. You’re trying to pull negative away from a positive and push negatives into a negative very soon after they touch.
Electricity, particularly at low voltages, needs to flow in a circuit, where it goes back to the place it started. If it doesn’t have that complete circuit, it doesn’t flow.
At high voltages, it can also flow into the ground, but battery voltages are much lower than that.
The battery is a pump. It just pushes the electricity. But when the “door” is closed, it’s just pushing against nothing and everything just stops. Putting two pumps one behind the other won’t make the water move if the door is still shut at the other end.
The way to “open” the door is to make a circuit… then the pump has somewhere to push the electricity, and the electricity has somewhere to go, and as it brushes past things in the circuit it does “work” (like light a lightbulb, or power a motor, or whatever).
If you imagine a wire as a set of ball-bearings in a tube, and air as an obstruction, then a circuit is a complete loop of ball bearings where the last eventually pushes on the first. When the circuit isn’t complete, you’re just pushing ball-bearings but they have nowhere to go. It’s like pushing them against a closed door (the air, which has a high resistance).
Only when you complete the circuit can the ENTIRE loop of ball-bearings move and it moves against itself… as one ball leaves the battery, another comes in behind, which means the whole loop is able to move around. And it’s that movement that is “electrical power”, that does useful work.
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