400 likes | 540 Views
Penetration depth of quasi-static H -field into a conductor. Section 59. Consider a good conductor in an external periodic magnetic field. The conductor is penetrated by the H -field, which induces a variable E-field, w hich causes “eddy” currents.
E N D
Penetration depth of quasi-static H-field into a conductor Section 59
Consider a good conductor in an external periodic magnetic field The conductor is penetrated by the H-field, which induces a variable E-field, which causes “eddy” currents.
Penetration of field is determined by the thermal conduction equation
Quiz: How does the propagation of heat depend on time? • Linearly • Quadratic • Square root
Quiz: How does the skin depth depend on frequency? • Inverse • Square root • Inverse Square root
Wavelength in metal is d not l, but d is also the characteristic damping length. Not much of a wave!
Quiz: At a given position within a conductor the low frequency limit, how does the electric field depend on frequency? • Increases linearly with f. • Increases as the square root of f. • Decreases as the inverse square root of f.
At a given position within a conductor the high frequency limit, how does the electric field depend on frequency? • Increases as Sqrt[f] • Decreases as Exp[-const*Sqrt[f]] • Decreases as Sqrt[f] *Exp[-const*Sqrt[f]]
Quiz: In low frequency fields, how does the rate of Joule heating for a metal depend on frequency? • Decreases as inverse square root of f • Increases linearly in f • Increases as f2
In high frequency fields, how does the rate of Joule heating for a metal depend on frequency? • Increases as square root of f • Decreases as 1/f • Increases as f2
A conductor acquires a magnetic moment in a periodic external H-field with the same period.
Quiz: What is a possible frequency dependence for the electric field at a given point inside a metal? .P