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

Stellen Sie sich eine Metallplatte vor, die an einem Ende befestigt ist und frei um ihre mittlere Position schwingt und zwischen zwei Elektromagneten platziert ist.
Wenn kein Magnetfeld vorhanden ist, oszilliert die Platte weiter. Sobald die Elektromagnete eingeschaltet sind, verlangsamt sich die Platte und stoppt schnell.
Diese Verringerung der Bewegung ohne physischen Kontakt wird als magnetische Dämpfung bezeichnet, die durch die entgegengesetzte Natur der Wirbelströme verursacht wird.
Schwingen Sie nun die Platte erneut, um diesen Mechanismus zu verstehen.
Wenn die Platte in das Magnetfeld eintritt, ändert sich der magnetische Fluss auf der Platte.
Nach dem Faradayschen Gesetz werden Wirbelströme in der Platte induziert, und nach dem Lenzschen Gesetz ist ihre Richtung gegen den Uhrzeigersinn. Die Platte erfährt also eine magnetische Kraft, die ihrer Bewegung entgegenwirkt.
Wenn die Platte das Magnetfeld verlässt, nimmt der magnetische Fluss ab und es werden Wirbelströme im Uhrzeigersinn induziert.
Dadurch erfährt die Platte wieder eine magnetische Kraft, die sich ihrem Austritt aus dem Magnetfeld entgegensetzt.
So werden als kombinierter Effekt die Schwingungen der metallischen Platte schnell gedämpft.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <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>

magnetische dämpfung

Eddyströme können eine signifikante Bremswirkung auf die Bewegung ausüben, die als magnetische Dämpfung bezeichnet wird. Wenn zum Beispiel ein metallischer Pendelkörper zwischen den Polen eines starken Magneten schwingt, wirkt eine erhebliche Bremskraft auf den Körper, wenn er in das Magnetfeld gelangt und dieses wieder verlässt, was die Bewegung schnell dämpft.

Wenn der Körper jedoch eine geschlitzte Metallplatte ist, hat der Magnet eine viel geringere Wirkung. Wenn eine geschlitzte Metallplatte in das Magnetfeld eindringt, wird eine elektromotorische Kraft durch die Änderung des Flusses induziert. Diese ist jedoch weniger effektiv, da die Schlitze die Größe der Stromschleifen begrenzen. Außerdem haben benachbarte Schleifen Ströme in entgegengesetzte Richtungen, und ihre Effekte heben sich gegenseitig auf. Bei Verwendung eines isolierenden Materials ist der Wirbelstrom äußerst gering, sodass die magnetische Dämpfung bei Isolatoren vernachlässigbar ist. Um Wirbelströme in Leitern zu vermeiden, müssen sie geschlitzt sein oder aus dünnen Schichten leitenden Materials bestehen, die durch isolierende Platten getrennt sind.

Die magnetische Dämpfung wird in empfindlichen Laborwaagen eingesetzt. Um ein Maximum an Empfindlichkeit und Genauigkeit zu erreichen, muss die Waage so reibungsfrei wie möglich sein. Wenn sie reibungsfrei ist, schwingt sie sehr lange. Die magnetische Dämpfung ist eine einfache und ideale Lösung. Bei der magnetischen Dämpfung ist der Luftwiderstand proportional zur Geschwindigkeit und wird bei einer Geschwindigkeit von Null null. Die Schwingungen werden also schnell gedämpft, danach verschwindet die Dämpfungskraft, so dass die Waage sehr empfindlich ist. In den meisten Waagen wird die magnetische Dämpfung durch eine leitende Scheibe erreicht, die in einem festen Feld rotiert.

Magnetische Dämpfung

Wirbelströme können einen erheblichen Bewegungswiderstand erzeugen, der als magnetische Dämpfung bezeichnet wird. Zum Beispiel, wenn ein metallisches Pendel zwischen den Polen eines ...

Education

Lehre

JoVE Core

Physik

Unit 1

Einheit 1

Electromagnetic Induction

Elektromagnetische Induktion

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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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lenz's law

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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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