Yes, Alternating current does not distribute uniformly over the cross-section of the conductor, but while with Direct current get distributed uniformly over the cross-section of the conductor. The reason for this phenomenon is the Skin effect.
Now due to skin effect the current get concentrated at the cross-section of the conductor, it does not distribute over the centre.
When current flows through the line then the magnetic field is produced around the conductor. The linkage of flux around the centre of the conductor is more than that at the outer periphery. Therefore inductance at the centre of the line is more than that at the periphery. So due to this high inductive reactance at the centre current do not flow from the centre but it tends to flow from less resistive path i.e. from the periphery of the conductor.
Thus, the reason for skin effect is inductive reactance of the line.
Now, this phenomenon is not observed in DC supply the reason is inductive reactance, as inductive reactance depends on the frequency but the frequency of DC supply is zero. So inductive reactance is also zero.
Thus it can also be said that skin effect directly or indirectly depends on the frequency of supply, when frequency increases skin effect will increase proportionally.
It also depends on the type of material of conductor and type of conductor. (I.e. its effect is more in the solid conductor as compared to stranded conductor)
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