Erratum: ’’Eddy currents: Levitation, metal detectors, and induction heating’’ [Am. J. Phys. 46, 464 (1978)]

Wouch, G.; Lord, Arthur E.

doi:10.1119/1.11731

Cited by 2 publications

(2 citation statements)

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“…within the sphere. We employ a common approximation, treating B m =0 to penetrate with no attenuation an outer layer of thickness δ of the conducting sphere and to be 0 further within (Wouch & Lord (1978), Chyba et al (2021)). An emf is generated around any path C (with line element dl) in this outermost layers of the conducting secondary for which C (v ϕ × B) • dl = 0.…”

Section: Azimuthal Velocitiesmentioning

confidence: 99%

Internal-Current Lorentz-Force Heating of Astrophysical Objects

Chyba,

Hand

2021

Preprint

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Two forms of ohmic heating of astrophysical secondaries have received particular attention: unipolargenerator heating with currents running between the primary and secondary; and magnetic induction heating due to the primary's time-varying field. Neither appears to cause significant dissipation in the contemporary solar system. But these discussions have overlooked heating derived from the spatial variation of the primary's field across the interior of the secondary. This leads to Lorentz force-driven currents around paths entirely internal to the secondary, with resulting ohmic heating. We examine three ways to drive such currents, by the cross product of: (1) the secondary's azimuthal orbital velocity with the non-axially symmetric field of the primary; (2) the radial velocity (due to non-zero eccentricity) of the secondary with the primary's field; or (3) the out-of-plane velocity (due to non-zero inclination) with the primary's field. The first of these operates even for a spin-locked secondary whose orbit has zero eccentricity, in strong contrast to tidal dissipation. We show that Jupiter's moon Io today could dissipate about 600 GW (more than likely current radiogenic heating) in the outer hundred meters of its metallic core by this mechanism. Had Io ever been at 3 jovian radii instead of its current 5.9, it could have been dissipating 15,000 GW. Ohmic dissipation provides a mechanism that could operate in any solar system to drive inward migration of secondaries that then necessarily comes to a halt upon reaching a sufficiently close distance to the primary.

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Section: Azimuthal Velocitiesmentioning

confidence: 99%

Internal-Current Lorentz-Force Heating of Astrophysical Objects

Chyba,

Hand

2021

Preprint

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“…It is clear that one is dealing with a transient phenomenon between the short-height cylindrical metallic conductors (the coins) and some magnetic field being generated in the interior of the wagon during the positive acceleration stage. It is either an effect related to the generation of Foucault (eddy) currents [4] in the metallic, therefore conducting, coins, caused by a quickly varying magnetic field and the subsequent orientation of the induced magnetic dipoles in the coins, or one is dealing with a simple transient magnetization [5][6][7] phenomenon of the material of which the short metallic cylinders are made via alignment of the permanent atomic dipoles of the material; that is, it could be a phenomenon involving matter magnetization and subsequent orientation of the total magnetic dipole in the external magnetic field.…”

Section: A Physical Model For the Phenomenonmentioning

confidence: 99%

An intriguing case of real-life physics: the tilting of Venezuelan coins in the Caracas Metro

Ladera

Millán

Paredes³

1998

Eur. J. Phys.

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We present an interesting and appealing phenomena, first observed by youngsters, which occurs when Venezuelan coins are placed on the floor of the passenger wagons of the Caracas Metro, the underground transportation system of the city. The phenomena - which consists of the upward tilting and occasional fast spinning of the coins, and even the formation of long chains of coins which can be made to hang from a hand - are excellent, highly motivating, examples of real-life physics and can be presented at different levels of education. To explain the behaviour of the coins, we construct a physical model, and then obtain the value of the magnetic dipole per atom in the coin, which is of the same order of magnitude as the Bohr magneton, the natural unit of the atomic magnetic dipole moment.

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Erratum: ’’Eddy currents: Levitation, metal detectors, and induction heating’’ [Am. J. Phys. 46, 464 (1978)]

Cited by 2 publications

References 0 publications

Internal-Current Lorentz-Force Heating of Astrophysical Objects

Internal-Current Lorentz-Force Heating of Astrophysical Objects

An intriguing case of real-life physics: the tilting of Venezuelan coins in the Caracas Metro

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