I'm quite confused about this actually! In fact, I had always thought current flows from a region of higher potential to a lower one. Does it have anything to do with the fact that it's a source of emf instead? What significance does that have?
[Physics] Why is it that for a source of emf, current flows from lower to higher potential
electric-circuitselectric-currentelectricity
Related Solutions
First the math:
Given the electric potential $V(\mathbf a)$ at a point $\mathbf a$ in space and the potential $V(\mathbf b)$ at another point $\mathbf b$, the electric potential energy of a charge moving from point $\mathbf a$ to point $\mathbf b$ will change by $$ U(\mathbf b) - U(\mathbf a) = q[V(\mathbf b) - V(\mathbf a)] $$ If the speed of an electron decreases in moving from a point $\mathbf a$ to a point $\mathbf b$, then that must mean that its potential energy has increased: $U(\mathbf b) - U(\mathbf a) >0$, so that since the electron has charge $-e$, we get $$ (-e)[V(\mathbf b) - V(\mathbf a)]>0 $$ which, upon dividing both sides by $-e$ (and noting to change the direction of the inequality when we do so) implies $$ V(\mathbf b) < V(\mathbf a) $$ So we see that the starting position $\mathbf a$ is at a higher potential than the final position $\mathbf b$ as the second paragraph says.
The intuition here is that there are some other charges around (they could be positive or negative depending on where we place them) that setup the potential "landscape" V in such a way that the potential at the origin, where the charge began, is higher than the potential at the final point, and a negative charge that rolls "down this potential hill" will be going slower when it gets to the bottom of the hill.
Hope that wasn't confusing!
Cheers!
To answer in terms of electric circuits, we know that electric field $\bf E$ is related to the electrical potential $V$ by
$${\bf E}=-{\bf \nabla} V$$
That means that a positively charged particle in a region with varying potential will experience a force pointing towards regions of lower potential (and a negatively charged particle will experience a force towards higher potentials). In either case we'd describe the result as a current from higher potential to lower potential.
But, it's not correct to say current always flows from high potential to low potential. Every circuit must include some current flowing from high potential to low potential, and some current flowing from low potential to high potential, in order to form a complete circuit. The circuit elements through which current flows from high to low potential consume electrical energy, converting it to some other form (or storing it temporarily). And the circuit elements through which current flows from low to high potential deliver electrical energy to the rest of the circuit, either converting it from some other form (as in a generator or battery) or releasing energy previously stored (as in a capacitor or inductor discharging).
In other systems, there are analogous processes of flow in both directions. For example, water only flows downhill (from higher to lower gravitational potential) because it previously was evaporated by solar energy and was transported to the higher potential region as water vapor and rain.
Best Answer
Within a source of emf like a battery a chemical reaction occurs which moves the mobile charge carriers from a region where they have low electric potential energy to a region where they have a higher electric potential energy.
If the charge carriers are positive that is taking those positive charge carriers from the negative terminal of the battery to the positive terminal whereas if the charge carriers are negative that is taking those negative charge carriers from the positive terminal of the battery to the negative terminal.
The source of emf can be thought of as a pump which raises the electric potential energy of the mobile charges at the expense of work being done which in the case of the battery is the chemical reaction whereas for a water pump it might be you turning a handle.