Name: current loops and torque in motors
Uploaded: 2023-04-30T12:41:03.000Z
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Physical Science

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Motion and Stability- Forces and Interactions

PS.PSc.6.4

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Force On A Current Loop In A Magnetic Field

Un dispositif électrique transformant l’énergie électrique en énergie mécanique est connu sous le nom de moteur à courant continu. Il se compose d’une partie fixe, le stator, et d’une partie rotative, le rotor.
Dans les moteurs, chaque boucle de fil est dans un champ magnétique ; lorsque le courant circule dans la boucle, les forces sur le fil le plus proche des pôles magnétiques sont dirigées dans des directions opposées, comme déterminé par la règle de la main droite. Le champ magnétique applique un couple, ce qui fait tourner l’arbre.
Considérons une boucle rectangulaire de fil porteur de courant avec des côtés de longueurs a et b dans un champ magnétique uniforme.
En rappelant la force magnétique sur une équation de fil porteur de courant droit, la force magnétique sur les côtés 1 et 3 peut être calculée, et la direction peut être déterminée à l’aide de la règle de la main droite.
De même, le courant sur les côtés 2 et 4 est perpendiculaire au champ magnétique, et donc, les forces sur ces côtés peuvent être déterminées.
Enfin, la force nette sur la boucle peut être calculée en additionnant toutes les forces de chaque côté de la boucle.

<ol>
	<li>OpenStax. (2019). Physique universitaire Vol. 2. [Version Web], p. 396 à 398. Tiré de <a href="https://openstax.org/books/university-physics-volume-2@8ede2ba/pages/11-4-magnetic-force-on-a-current-carrying-conductor">https://openstax.org/books/university-physics-volume-2@8ede2ba/pages/11-4-magnetic-force-on-a-current-carrying-conductor</a></li>
</ol>

force sur une boucle de courant dans un champ magnétique

Les forces magnétiques sur les fils transportant du courant sont le plus souvent utilisées dans les moteurs. Un moteur à courant continu est un dispositif qui convertit l'énergie électrique en travail mécanique. Dans les moteurs, des boucles de fils sont enfermées dans un champ magnétique. Lorsque du courant circule à travers les boucles, le champ magnétique applique un couple, ce qui fait tourner l'arbre du moteur. La direction du courant est inversée une fois que la surface de la boucle est alignée avec le champ magnétique, créant un couple constant sur la boucle. Pendant le processus, des commutateurs et des balais sont utilisés pour inverser le courant. Le commutateur est réglé pour inverser le flux de courant à certains points afin de maintenir un mouvement continu dans le moteur. Un commutateur de base comporte trois zones de contact pour éviter les points morts où la boucle aurait un couple instantané nul à cet endroit. Les balais appuient contre le commutateur, créant un contact électrique entre les parties du commutateur pendant le mouvement de rotation.

Considérons une boucle de fil de forme rectangulaire avec des côtés de longueurs a et b, telle qu'une boucle dans un moteur, placée dans un champ magnétique uniforme, comme le montre la figure 1.

<img alt="Equation1" src="/files/ftp_upload/13770/13770_PT_figure.svg" style="text-align: center; height: 250px;" />

La boucle de fil subit des forces qui peuvent être calculées en appliquant l'équation de la force magnétique sur un fil droit portant du courant à chacun des côtés. La force sur le côté 1 et sur le côté 2 peut être calculée comme suit:

<img alt="Equation1" src="/files/ftp_upload/13770/13770_Equation_1.svg" style="text-align: center; height: 18px;" />

<img alt="Equation2" src="/files/ftp_upload/13770/13770_Equation_2.svg" style="text-align: center; height: 18px;" />

La magnitude du courant sur le côté 3 et sur le côté 4 est la même mais circule dans la direction opposée à celle sur le côté 1 et sur le côté 2, respectivement. Ainsi, la force sur le côté 3 et sur le côté 4 est égale à la force sur le côté 1 et sur le côté 2, respectivement, avec un signe négatif. Enfin, la force totale dans la boucle de fil portant du courant est égale à la somme des forces individuelles agissant sur chaque côté de la boucle et peut être calculée comme suit:

<img alt="Equation3" src="/files/ftp_upload/13770/13770_Equation_3.svg" style="text-align: center; height: 18px;" />

Force sur une boucle de courant dans un champ magnétique

Les forces magnétiques sur les fils transportant le courant sont le plus souvent appliquées dans les moteurs. Un moteur à courant continu est un appareil qui convertit l’énergie électrique en ...

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current loops and torque in motors

Current loops in a magnetic field create the torque that drives a DC motor. A DC motor converts electrical energy into mechanical work. In a motor, wire loops sit inside a magnetic field. When current flows through the loops, the magnetic field pushes on them and makes the shaft rotate.

The current is reversed when the loop lines up with the magnetic field. This keeps the torque on the loop going in the same direction. A commutator and brushes handle this reversal. The commutator switches the current flow at specific points, and the brushes keep electrical contact as the parts spin.

A basic commutator has three contact areas. This design helps avoid dead spots, which are points where the loop would have zero instantaneous torque. A rectangular loop of wire is a simple model for this process. If the loop has sides a and b and is placed in a uniform magnetic field, each side feels a magnetic force.

The force on each side can be found by applying the magnetic force equation for a straight current-carrying wire. The current on side 3 and side 4 has the same magnitude as on side 1 and side 2, but it flows in the opposite direction. That means the forces on side 3 and side 4 are equal to those on side 1 and side 2, but with a negative sign. The total force on the loop is the sum of the forces on all four sides.

Current Loops and Torque in Motors

magnetism

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magnetic fields

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Reading Magnetic Field Lines

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magnetic force on a current-carrying conductor

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magnetic force on current-carrying wires: example

magnetic-force-on-current-carrying-wires-example

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Magnetic force can balance the weight of a current-carrying wire when the wire sits in a magnetic field. Moving charges in the wire feel a force, so the wire itself can be pushed upward or downward. This example uses a flexible wire that is 40 cm long and has a mass of 10 g. It is held in a horizontal position inside a constant 0.40 T magnetic field. The goal is to find the current needed to remove the tension in the supporting leads. To do that, a free-body diagram is drawn first. The diagram...

force on a current loop in a magnetic field

Current loops in a magnetic field create the torque that drives a DC motor. A DC motor converts electrical energy into mechanical work. In a motor, wire loops sit inside a magnetic field. When current flows through the loops, the magnetic field pushes on them and makes the shaft rotate. The current is reversed when the loop lines up with the magnetic field. This keeps the torque on the loop going in the same direction. A commutator and brushes handle this reversal. The commutator switches the...

torque on a current loop in a magnetic field

torque-on-a-current-loop-in-a-magnetic-field

Current Loop Torque in Electric Motors

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Learn how current loops in a magnetic field create torque in a DC motor, and how commutators and brushes keep the shaft turning.

Current Loops and Torque in Motors | JoVE K12

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Current Loops and Torque in Motors

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