Generators convert mechanical energy into electrical energy, whereas motors convert electrical energy into mechanical energy. A motor works by sending a current through a loop of wire located in a magnetic field. As a result, the magnetic field exerts a torque on the loop. This rotates a shaft, extracting mechanical work from the electrical current sent in initially. When the coil of a motor is turned, magnetic flux changes through the coil, and an emf (consistent with Faraday's law) is induced. The motor thus acts as a generator whenever its coil rotates. This happens whether the shaft is turned by an external input, like a belt drive, or by the action of the motor itself. When a motor is doing work, and its shaft is turning, an emf is generated. Lenz's law states that the emf opposes any change, so the input emf that powers the motor is opposed by the motor's self-generated emf, called the back emf of the motor.

The generator output of a motor is the difference between the supply voltage and the back emf. The back emf is zero when the motor is first turned on, meaning that the coil receives the full driving voltage, and the motor draws maximum current when it is on but not turning. As the motor spins faster, the back emf grows, always opposing the driving emf. This reduces the voltage across the coil and the amount of current it draws.

When a motor first comes on, it draws more current than when it runs at its normal operating speed. When a mechanical load is placed on the motor, like an electric wheelchair going up a hill, the motor slows, the back emf drops, more current flows, and more work can be done. If the motor runs at too low a speed, the larger current can overheat it, perhaps even burning it out. On the other hand, if there is no mechanical load on the motor, it increases its angular velocity until the back emf is nearly equal to the driving emf. Then the motor uses only enough energy to overcome friction.

Tags
Back EMFGeneratorsMotorsMechanical EnergyElectrical EnergyMagnetic FieldTorqueFaraday s LawInduced EmfLenz s LawSupply VoltageCurrent DrawMechanical LoadAngular VelocityFriction

Du chapitre 30:

article

Now Playing

30.18 : Back EMF

Electromagnetic Induction

2.5K Vues

article

30.1 : Induction

Electromagnetic Induction

3.6K Vues

article

30.2 : Loi de Faraday

Electromagnetic Induction

3.6K Vues

article

30.3 : Loi de Lenz

Electromagnetic Induction

3.2K Vues

article

30.4 : F.Emf mobile

Electromagnetic Induction

2.9K Vues

article

30.5 : Dynamo de disque Faraday

Electromagnetic Induction

1.9K Vues

article

30.6 : Champs électriques induits

Electromagnetic Induction

3.2K Vues

article

30.7 : Champs électriques induits : applications

Electromagnetic Induction

1.2K Vues

article

30.8 : Courants de Foucault

Electromagnetic Induction

1.3K Vues

article

30.9 : Courant de déplacement

Electromagnetic Induction

2.6K Vues

article

30.10 : Importance du courant de déplacement

Electromagnetic Induction

4.1K Vues

article

30.11 : Champs électromagnétiques

Electromagnetic Induction

2.0K Vues

article

30.12 : Équation de Maxwell de l’électromagnétisme

Electromagnetic Induction

2.8K Vues

article

30.13 : Symétrie dans les équations de Maxwell

Electromagnetic Induction

3.1K Vues

article

30.14 : Loi d’Ampère-Maxwell : résolution de problèmes

Electromagnetic Induction

368 Vues

See More

JoVE Logo

Confidentialité

Conditions d'utilisation

Politiques

Recherche

Enseignement

À PROPOS DE JoVE

Copyright © 2025 MyJoVE Corporation. Tous droits réservés.