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The fact that current density is higher at the surface when compared to centre is known as
Skin effect
Proximity effect
Corona effect
None of the above
Skin effect
The skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is highest near the surface and decreases exponentially towards the center. This occurs because internal magnetic flux linkages are stronger at the center, causing higher self-inductance and thus higher impedance at the core.
The skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is highest near the surface and decreases exponentially towards the center. This occurs because internal magnetic flux linkages are stronger at the center, causing higher self-inductance and thus higher impedance at the core.
J(x)=JsтАЛeтИТ╬┤xтАЛ тАФ current density at depth x from surface
╬┤=╧Й╬╝2╧БтАЛтАЛ тАФ skin depth representing the distance at which current density falls to 37% of its surface value
When AC flows through a conductor, it produces a time-varying magnetic field that induces eddy currents. These eddy currents oppose the flow of current at the center of the conductor and aid it near the surface. Consequently, the conductor's effective resistance increases, as the interior material carries less current, effectively reducing the cross-sectional area available for conduction.
Skin effect increases with higher frequency, higher magnetic permeability, and higher conductivity.
The effect is negligible in DC circuits where current distribution is uniform.
Skin depth ╬┤ is inversely proportional to the square root of frequency.
For power transmission at 50Hz, the skin effect is relatively small but significant for large-diameter conductors.
Used in surface hardening of metals by induction heating
Reduces interference in communication cables
Increases effective AC resistance of power lines
Leads to increased I2R power losses in conductors
Design of high-frequency waveguides and antennas
High-power transmission line cable design
Induction furnace design
Proximity effect is the distortion of current distribution due to magnetic fields of nearby conductors.
Corona effect is the ionization of air surrounding a conductor, leading to power loss and audible noise.
A is correct тАФ The skin effect refers to the non-uniform distribution of AC current where density is highest at the outer surface of the conductor.
Always remember that skin effect is frequency-dependent; for f=0 (DC), the skin depth is infinite, resulting in uniform current distribution.