I think it is useful to understand the cause of the skin effect.
Let me begin with debunking the often quoted, but incorrect, statement that there is no current flowing at the center of the wire carrying AC current. A slightly more correct statement would be that there is no useful current. Because the truth is, that there IS current flowing in the center, it's just going in the wrong direction.
When an AC current is flowing in a wire, it generates a magnetic field which rises and falls. If the wire is the primary winding of a transformer, this rising and falling magnetic field will induce a current in the secondary winding. But, even in the absence of a transformer core, or even a second wire, the magnetic field still rises and falls. And when moving magnetic field cuts through a conductor, a current will be generated, even if it's the same wire that is carrying the original current. These are called eddy currents. And it is the eddy current in a wire that causes the AC resistance to be larger than the DC resistance would be for the same wire.
For a given frequency, a larger diameter wire gives more area for the magnetic field to work in,making stronger eddy currents. And stronger the eddy currents give the wire a higher AC to DC resistance ratio.
Let me begin with debunking the often quoted, but incorrect, statement that there is no current flowing at the center of the wire carrying AC current. A slightly more correct statement would be that there is no useful current. Because the truth is, that there IS current flowing in the center, it's just going in the wrong direction.
When an AC current is flowing in a wire, it generates a magnetic field which rises and falls. If the wire is the primary winding of a transformer, this rising and falling magnetic field will induce a current in the secondary winding. But, even in the absence of a transformer core, or even a second wire, the magnetic field still rises and falls. And when moving magnetic field cuts through a conductor, a current will be generated, even if it's the same wire that is carrying the original current. These are called eddy currents. And it is the eddy current in a wire that causes the AC resistance to be larger than the DC resistance would be for the same wire.
For a given frequency, a larger diameter wire gives more area for the magnetic field to work in,making stronger eddy currents. And stronger the eddy currents give the wire a higher AC to DC resistance ratio.