Correct Answer - Option 4 : All of these
Skin effect is the tendency of an alternating electric current to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases with greater depths in the conductor.
The electric current flows mainly at the skin of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor.
Proximity Effect:
The alternating flux in a conductor is caused by the current of the other nearby conductor. This flux produces a circulating current or eddy current in the conductor which results in an apparent increase in the resistance of the wire. Thus, more power losses in the windings. This phenomenon is called the proximity effect.
Eddy current losses are also accounts for increasing ac resistance.
