Does electricity travel through the wire or on the outer surface?
Majority moves through the wires as current, the exterior electricity on the outside is slim to none, therfore it can be ignored.
All electrical current produce Electro-Motive Force.
All currents produce EMF in the same orientation.
Like EMF repel each other.
This means that if you have two wires side by side conducting the same AC currents, that they will repel each other.
Within each wire, you can think of the wire as being made up of a bundle of smaller wires. The current in each of the smaller wires will repel the other wires, or the currents in them.
Thus the current flow in a wire is concentrated on the surface of the wire, as the current in the middle is repelled more than any other currents.
Normally the effect is negligle, but design of high current wires is tricky.
The electricity or current travels in the outer surface. Why? Let say will take some example of an element atom where we have the nucleus, protons and electrons. From our basic knowledge that electrons stays at the outer shell and the outermost electrons or the valence electrons have the chance to move freely which also responsible of carrying negative or electric charge.
Back to your question now, same principle as discussed above that the electrons stays at the outermost shell which responsible of carrying electricity or current. When voltage induced in you outlet, current produced and the outermost electrons in your wire gain some electric charged which increases there energy to move freely at the surface.
