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As frequency increases Depth of penetration
Increases
Decreases
Both
None
Decreases
Depth of penetration, often referred to as the skin depth, is inversely proportional to the square root of the operating frequency in induction heating and electromagnetic applications. As the frequency of the alternating current increases, the magnetic field induces eddy currents that are confined more strictly to the surface of the conductor, resulting in a reduced depth of penetration.
Depth of penetration, often referred to as the skin depth, is inversely proportional to the square root of the operating frequency in induction heating and electromagnetic applications. As the frequency of the alternating current increases, the magnetic field induces eddy currents that are confined more strictly to the surface of the conductor, resulting in a reduced depth of penetration.
╬┤=╧Аf╬╝╧ГтАЛ1тАЛ тАФ where ╬┤ is skin depth, f is frequency, ╬╝ is permeability, and ╧Г is conductivity.
The mechanism is driven by the skin effect, where eddy currents generate a secondary magnetic field that opposes the main current flow at the center of the conductor. As frequency increases, the reactance X=2╧АfL rises, forcing current to flow through the path of least impedance, which is the surface layer. Mathematically, the depth ╬┤ is defined as ╬┤=╧Аf╬╝╧Г1тАЛтАЛ.
Higher frequency causes deeper concentration of current at the surface.
The phenomenon is known as the Skin Effect.
Effective resistance of the conductor increases as depth of penetration decreases.
Surface hardening of steel can be controlled by frequency selection.
Efficient use of induction for shallow heat treatment.
Higher frequency leads to increased ohmic losses due to reduced effective cross-sectional area.
Requires high-frequency power electronics (inverters).
Induction Surface Hardening
High-frequency welding
RF shielding
At DC (f=0), the depth of penetration is theoretically infinite, meaning current is distributed uniformly.
Option B is correct because the inverse square root relationship dictates that higher f leads to lower ╬┤.
B is correct тАФ As frequency increases, the skin effect becomes more pronounced, causing the current to concentrate on the surface and reducing the depth of penetration.
Always remember that in induction heating, selecting the correct frequency is a trade-off between the required heating depth and electrical efficiency.