Name: eddy currents and magnetic braking
Uploaded: 2023-09-18T17:11:20.000Z
Duration: 1 min 17 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Physics

motion-and-stability-forces-and-interactions

Motion and Stability- Forces and Interactions

PS.Phy.5.2

Magnetic Damping

Si consideri una piastra metallica fissata a un'estremità che oscilla liberamente nella sua posizione media, posta tra due elettromagneti.
Quando non c'è campo magnetico, la piastra continua a oscillare. Una volta accesi gli elettromagneti, la piastra rallenta e si ferma rapidamente.
Questa riduzione del movimento senza alcun contatto fisico è chiamata smorzamento magnetico, causato dalla natura opposta delle correnti parassite.
Ora fai oscillare di nuovo la piastra per capire questo meccanismo.
Quando la lastra entra nel campo magnetico, il flusso magnetico sulla lastra cambia.
Secondo la legge di Faraday, le correnti parassite sono indotte nella piastra e, secondo la legge di Lenz, la loro direzione è in senso antiorario. Quindi, la piastra subisce una forza magnetica che si oppone al suo movimento.
Allo stesso modo, quando la lastra esce dal campo magnetico, il flusso magnetico diminuisce e le correnti parassite vengono indotte in senso orario.
Di conseguenza, la placca subisce nuovamente una forza magnetica che si oppone alla sua uscita dal campo magnetico.
Quindi, come effetto combinato, le oscillazioni della piastra metallica vengono rapidamente smorzate.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/13-5-eddy-currents">https://openstax.org/books/university-physics-volume-2/pages/13-5-eddy-currents</a></li>
</ol>

smorzamento magnetico

L'effetto delle correnti parassite può produrre una significativa resistenza al moto, denominata smorzamento magnetico. Ad esempio, quando un pendolo metallico oscilla tra i poli di un magnete forte, si verifica una resistenza significativa sul pendolo mentre entra e esce dal campo magnetico, smorzando rapidamente il moto.

Tuttavia, se il pendolo è una lamiera metallica scanalata, l'effetto magnetico è molto più ridotto. Quando una lamiera metallica scanalata entra nel campo, si induce una f.m.i. a causa della variazione di flusso; tuttavia, è meno efficace perché le scanalature limitano le dimensioni dei circuiti di corrente. Inoltre, i circuiti adiacenti hanno correnti in direzioni opposte e i loro effetti si annullano. Quando viene utilizzato un materiale isolante, la corrente parassita è estremamente piccola, quindi lo smorzamento magnetico sugli isolanti è trascurabile. Se si vogliono evitare le correnti parassite nei conduttori, devono essere scanalati o costruiti con sottili strati di materiale conduttore separati da fogli isolanti.

Lo smorzamento magnetico è utilizzato nelle bilance di laboratorio sensibili. Per massimizzare la sensibilità e l'accuratezza, la bilancia deve essere il più possibile priva di attrito. Se è priva di attrito, oscilla per un tempo molto lungo. Lo smorzamento magnetico è una soluzione semplice e ideale. Con lo smorzamento magnetico, la resistenza è proporzionale alla velocità e diventa zero a velocità zero. Di conseguenza, le oscillazioni vengono rapidamente smorzate, dopodiché la forza di smorzamento scompare, consentendo alla bilancia di essere molto sensibile. Nella maggior parte delle bilance, lo smorzamento magnetico viene realizzato con un disco conduttore che ruota in un campo fisso.

Smorzamento magnetico

Le correnti parassite possono produrre una resistenza significativa sul movimento, chiamata smorzamento magnetico. Ad esempio, quando un pendolo metallico oscilla tra i pali di un ...

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Fisica

Unit 1

Unità 1

Electromagnetic Induction

Induzione elettromagnetica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

eddy currents and magnetic braking

Eddy currents can create strong drag on moving objects. This drag is called magnetic damping. A metallic pendulum bob swinging between the poles of a strong magnet feels this force as it enters and leaves the field, so its motion dies out quickly.

The effect is much smaller for a slotted metal plate. As the plate enters the magnetic field, a changing flux induces an emf, or electromotive force. The slots limit the size of the current loops, and nearby loops can carry currents in opposite directions, so their effects cancel.

Insulating materials behave differently. Their eddy currents are extremely small, so magnetic damping on insulators is negligible. If eddy currents must be reduced in conductors, the material can be slotted or made from thin conducting layers separated by insulating sheets.

Magnetic damping is useful in sensitive laboratory balances. These balances need to be as friction-free as possible for maximum sensitivity and accuracy. A friction-free balance can oscillate for a long time, so magnetic damping provides a simple solution. The drag is proportional to speed and drops to zero when the object stops moving, which quickly calms the motion while keeping the balance sensitive. In most balances, this is done with a conducting disc rotating in a fixed magnetic field.

Eddy Currents and Magnetic Braking

induction

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magnetic damping

Eddy currents can create strong drag on moving objects. This drag is called magnetic damping. A metallic pendulum bob swinging between the poles of a strong magnet feels this force as it enters and leaves the field, so its motion dies out quickly. The effect is much smaller for a slotted metal plate. As the plate enters the magnetic field, a changing flux induces an emf, or electromotive force. The slots limit the size of the current loops, and nearby loops can carry currents in opposite...

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Learn how eddy currents create magnetic damping, why slotted plates reduce the effect, and how balances use it to improve sensitivity and accuracy.

Eddy Currents and Magnetic Braking | JoVE K12

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Eddy Currents and Magnetic Braking

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