Current flow stops at battery's positive terminal?

Question

So let's take this circuit:

To find voltage across \$ V_1 \$, you do KVL in loop 1 to find \$ V_1 \$

you say:

\$ 5V + V_1 + V_3 = 0 \$

correct? But why is it assumed that current flows through the 5V supply? Aren't the positive and negative terminals of the battery (5V supply in this case) separated? Current direction defined as flowing from the positive terminal to negative terminal, but let's ignore that, and talk about what happens in reality. Physically, electrons will go from the negative terminal of the 5V supply around the loop to the positive terminal of 5V supply.

So, the 5V supply is really an open circuit, isn't it? Whenever you do KVL or these loop equations, why is it assumed that current flows seamlessly between voltage supplies?

Answer 1

First, Kirchoff's Voltage Law (KVL) applies whether there's current flowing through the branches you traverse or not. In your circuit you could replace R3 with an open circuit, and replace R2 with an arbitrary network or resistors, transistors, etc., and your KVL equation would still hold: \$5\ {\rm V}+V_1+V_3=0\$. It wouldn't be much use for calculating the branch currents because you wouldn't be able to write \$V_3\$ in terms of branch currents, but it would still be a valid equation.

Second, current does flow through the battery. It doesn't flow as electron current in a metal, but as ions flowing through the battery's dielectric.