Faraday's Disk Dynamo: why is there an emf?

In summary, the conversation discusses Faraday's law and a situation involving a rotating disk on a uniform magnetic field. The law states that there should be no emf in this situation, but the individual is questioning why there appears to be one. It is explained that the apparent paradox is due to a changing area when a valid conduction path is chosen, leading to a change in flux despite the constant magnetic field.
  • #1
jpas
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Consider a rotating disk on a uniform magnetic field. Faraday's law states that

[tex] \epsilon = - \frac{d\phi}{dt}[/tex]

In this situation, [tex]\vec B[/tex] is constant and the area of the disk is constant. Hence, the magnetic flux is constant and there should be no emf. What am I missing?
 
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  • #2
jpas said:
Consider a rotating disk on a uniform magnetic field. Faraday's law states that

[tex] \epsilon = - \frac{d\phi}{dt}[/tex]

In this situation, [tex]\vec B[/tex] is constant and the area of the disk is constant. Hence, the magnetic flux is constant and there should be no emf. What am I missing?

This question is common and has been discussed in several threads previously.

This is one of those tricky situations that appears paradoxical, but really isn't. This paper provides a good explanation.

Basically, even though the field could be considered constant, the total flux includes area. The area also appears constant at first, but as this paper shows, the conduction path usually chosen is not valid. In reality, the area is changing if a valid conduction path is chosen. And, changing area with constant field gives rise to a flux change.
 

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1. Why does Faraday's Disk Dynamo produce an emf?

Faraday's Disk Dynamo produces an emf (electromotive force) because of the movement of conductive material, such as liquid metal or plasma, through a magnetic field. This movement creates a change in magnetic flux, which in turn induces an electric field and produces an emf.

2. How does the emf in Faraday's Disk Dynamo work?

The emf in Faraday's Disk Dynamo works through the process of electromagnetic induction. As the conductive material moves through the magnetic field, it creates a change in magnetic flux, which generates an electric field. This electric field then drives the flow of electrons, resulting in an emf.

3. What factors affect the emf produced by Faraday's Disk Dynamo?

The emf produced by Faraday's Disk Dynamo can be affected by several factors, including the speed of the conductive material, the strength of the magnetic field, and the number of turns in the dynamo. Additionally, the shape and size of the dynamo can also impact the emf produced.

4. How is Faraday's Disk Dynamo different from other types of dynamos?

Faraday's Disk Dynamo is different from other types of dynamos because it uses a rotating disk of conductive material to generate an emf, whereas other dynamos may use different methods, such as moving a wire or rotating a magnet. Additionally, Faraday's Disk Dynamo relies on electromagnetic induction, while other dynamos may use other principles, such as static electricity or chemical reactions.

5. What are the real-world applications of Faraday's Disk Dynamo and its emf production?

Faraday's Disk Dynamo has several real-world applications, including power generation, electric motors, and generators. The emf produced by the dynamo can be harnessed to power various devices and machinery, making it a crucial technology in modern society.

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