batterieselectric-circuitshomework-and-exercises
Here is a drawing of the circuit that is confusing me:
I don't quite understand how batteries work in this diagram. If a battery has a negative and positive terminal, there must be a barrier preventing them from neutralizing one another, so how can the potential from either negative terminal ever make it through the top half of the circuit without passing through a battery?
I think this picture answers the question:
The battery's terminals are not charged. It's just a chemical reaction that starts the charge.
There's a $\text{Zn}$ and a $\text{CuSO}_4$. When they meet each other via a cable, the $\text{Zn}$ gives 2 electrons to $\text{CuSO}_4$ and becomes $\text{Zn}^{2+}$.
$\text{Cu}^{2+}$ of $\text{CuSO}_4$ becomes $\text{Cu}$ and becomes electrostatically neutral, and separates from $\text{SO}_4^{2-}$.
Then we have $\text{SO}_4$ with -2 charge and $\text{Zn}$ with +2 charge. So, $\text{SO}_4^{2-}$ moves to $\text{Zn}^{2+}$ to get bound to each other.
In the end, we have $\text{ZnSO}_4$ and $\text{Cu}$.
With two different batteries, it's not possible. The $\text{SO}_4^{2-}$ has nowhere to go and make new connections. Thus the chemical and electrical process doesn't start.
The potential difference exists between the two plates of the same battery. You don't know for sure if the potential difference exists between two plates from different batteries.
Additionally, you're not allowing any current to flow even if there is some potential difference. In other words, you have not closed the circuit. Current can't flow in a circuit that's not closed.
Best Answer
To put Zetta's answer in more visual terms: A battery "pushes out" electrons on the negative pole while "sucking in" electrons on the positive side. In the diagram you draw the 9V battery pushes electrons way more strongly than the 3V battery, so they move from the 9V to the 3V.
An analogy with tilted boards may also help: Suppose you tilt a board to the left and put a ball on it, on the ground floor of a building. It will roll to the left. If you put the same board on the second floor, but tilt it to the right, the ball will roll to the right, even though both ends of the board are now located higher than before.
What matters is not the absolute value, but the difference!