30.11
Dynamo à disque de Faraday
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Q1: How does a Faraday disk dynamo generate electrical current?
A Faraday disk dynamo generates current through motional emf. As a conducting disk rotates in a perpendicular magnetic field, the magnetic force pushes positive charges toward the rim and negative charges toward the center. This charge separation creates an emf that drives current through an external circuit via stationary brushes connected to the disk's rim and center.
Q2: Why does external work need to be supplied to keep the disk rotating?
According to Lenz's law, the induced current opposes the cause producing it. In a Faraday disk dynamo, the induced current creates a magnetic force that opposes the disk's rotation. Therefore, external work must continuously be supplied to maintain constant angular velocity against this opposing force.
Q3: What role do brushes play in a Faraday disk dynamo?
Brushes are stationary conductors that connect the rotating disk to an external circuit. They maintain electrical contact with the disk's rim and center, allowing the induced current to flow through the closed loop. This connection enables the dynamo to deliver electrical power to external devices.
Q4: How can the induced emf in a Faraday disk dynamo be increased?
The induced emf can be enhanced by increasing the magnetic field strength, the disk's radius, or the disk's angular velocity. Additionally, connecting multiple generators in series increases total emf output. These modifications amplify the charge separation and voltage generation within the dynamo.
Q5: What is the relationship between magnetic flux change and emf in this device?
As the disk rotates, the magnetic flux through different disk segments changes continuously. This changing flux induces an emf according to electromagnetic induction principles. The rotation ensures constant flux variation, producing a steady direct current output rather than alternating current.
Q6: Why is a Faraday disk dynamo classified as a DC generator?
A Faraday disk dynamo produces a constant emf in time, making it a direct current generator. Unlike alternating current generators, the charge distribution on the disk remains consistent as it rotates, resulting in unidirectional current flow through the external circuit.
Q7: How does the magnetic field orientation affect the polarity of induced emf?
The direction of the magnetic field and the direction of disk rotation together determine the polarity of the induced emf. Reversing either the field direction or rotation direction reverses the polarity, changing which terminal becomes positive or negative in the external circuit.