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

K12 Standards

north-carolina-k-12-science-standard-course-of-study

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

Considérons une plaque métallique fixée à une extrémité se balançant librement autour de sa position moyenne, placée entre deux électroaimants.
Lorsqu’il n’y a pas de champ magnétique, la plaque continue d’osciller. Une fois les électroaimants allumés, la plaque ralentit et s’arrête rapidement.
Cette réduction du mouvement sans aucun contact physique est appelée amortissement magnétique, causée par la nature opposée des courants de Foucault.
Maintenant, balancez à nouveau la plaque pour comprendre ce mécanisme.
Lorsque la plaque entre dans le champ magnétique, le flux magnétique sur la plaque change.
Selon la loi de Faraday, les courants de Foucault sont induits dans la plaque, et selon la loi de Lenz, leur direction est dans le sens inverse des aiguilles d'une montre. Ainsi, la plaque subit une force magnétique qui s’oppose à son mouvement.
De même, lorsque la plaque sort du champ magnétique, le flux magnétique diminue et les courants de Foucault sont induits dans le sens des aiguilles d’une montre.
En conséquence, la plaque subit à nouveau une force magnétique qui s’oppose à sa sortie du champ magnétique.
Ainsi, en tant qu’effet combiné, les oscillations de la plaque métallique sont rapidement amorties.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web]. Récupéré de <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>

amortissement magnétique

Les courants de Foucault peuvent produire une traînée significative sur le mouvement, appelée amortissement magnétique. Par exemple, lorsqu'une masse pendulaire métallique oscille entre les pôles d'un aimant puissant, une traînée importante agit sur la masse lorsqu'elle entre et quitte le champ, amortissant rapidement le mouvement.

Toutefois, si la masse est une plaque métallique découpée, l'aimant produit un effet beaucoup plus faible. Lorsqu'une plaque métallique découpée entre dans le champ, une fem est induite par le changement de flux; cependant, elle est moins efficace car les fentes limitent la taille des boucles de courant. De plus, les boucles adjacentes ont des courants dans des directions opposées, et leurs effets s'annulent. Lorsqu'un matériau isolant est utilisé, le courant de Foucault est extrêmement faible, de sorte que l'amortissement magnétique sur les isolants est négligeable. Si les courants de Foucault doivent être évités dans les conducteurs, ils doivent être découpés ou être constitués de fines couches de matériau conducteur séparées par des feuilles isolantes.

L'amortissement magnétique est utilisé dans des balances de laboratoire sensibles. Pour avoir une sensibilité et une précision maximales, la balance doit être aussi exempt de frottement que possible. S'il est exempt de frottement, il oscille pendant très longtemps. L'amortissement magnétique est une solution simple et idéale. Avec l'amortissement magnétique, la traînée est proportionnelle à la vélocité et devient nulle à une vélocité nulle. Ainsi, les oscillations sont rapidement amorties, après quoi la force d'amortissement disparaît, permettant à la balance d'être très sensible. Dans la plupart des balances, l'amortissement magnétique est réalisé avec un disque conducteur qui tourne dans un champ fixe.

Amortissement magnétique

Les courants de Foucault peuvent produire une traînée importante sur le mouvement, appelée amortissement magnétique. Par exemple, lorsqu’un pendule métallique se balance entre les pôles d’un ...

Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Electromagnetic Induction

Induction électromagnétique

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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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electromagnetic fields

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key terms and concepts

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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