Need help with a thought experiment about a Faraday generator

In summary: Instead, the charges are moving at a constant velocity along the circumference of the disk, resulting in a constant magnetic field and no induced current. Additionally, the switching of MOSFETS will not generate any extra energy as it is only controlling the path of the current, not creating it. Therefore, this idea does not work and does not violate any fundamental laws of physics. In summary, the idea of using multiple closely spaced individual contacts attached to MOSFETS to simulate a rotating carbon contact brush and generate extra energy does not work due to the constant velocity of the charges in the disk and the fact that the MOSFETS only control the path of the current, not create it.
  • #1
girts
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Hi, I arrived at a paradox today which I cannot explain myself. I was watching some physics videos on youtube and among them some were about lenz law and faraday disc workings.
Now I know and understand the classical examples of why there is current generated when the magnet moves together with the disc and otherwise, I can even understand that there is also current generated if the disc, magnet stay stationary but only the current collecting brushes are moved, and then even just one of them - the perimeter outer one as the one on the rotor shaft can be left stationary since at the midpoint of the disc there is no force on the electrons and then the force increases as we move more to the perimeter.

So technically if we take the load and the perimeter brush, we can rotate the perimeter brush around the disc perimeter or circumference and leave the other brush at the center stationary and we would have current through our load , because as we move the outer brush an imaginative wire is dragged around a uniform B field which exerts a force on the electrons in the wire or in this case in the shortest path between the middle of the disc and the outer circumference brush.
Now I would like to explain the part which I don't understand and which I though up myself today.
What happens if we substitute the circumference brush contact with multiple closely spaced individual contacts that are attached to an array of switches (MOSFETS) and now we attach the mosfets to a driver signal which makes them turn on and off one after another so that they turn on and off going in a circular path around the disc, we would switch them on and off in such a manner that at all times there is atleast two mosfets switched on simultaneously and as the previous one is switched off the next one after the one that is still on is switched on.
This action would essentially resemble a carbon contact brush moving around the disc circumference only here there would be no physical movement, but still our imaginative wire which is the shortest path of resistance between the center and the rim would be there formed through the constant switching of the mosfets.

The problem here is that switching mosfets on and off requires very little power compared to the power generated in a rotating copper disc in a uniform B field so this would imply that we could get extra energy out and essentially brake some fundamental laws of physics, so please explain me the best you can why this doesn't work, I'm really curious where my thinking goes black here?thanks.
 
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  • #2
The issue is in this statement
girts said:
So technically if we take the load and the perimeter brush, we can rotate the perimeter brush around the disc perimeter or circumference and leave the other brush at the center stationary and we would have current through our load
This will not generate a current since the charges in the disk are not moving through the magnetic field and thus experience no Lorentz force.
 

Related to Need help with a thought experiment about a Faraday generator

1. What is a Faraday generator?

A Faraday generator, also known as a Faraday disc, is a device that converts mechanical energy into electrical energy through the use of electromagnetic induction. It was invented by Michael Faraday in 1831.

2. How does a Faraday generator work?

A Faraday generator works by rotating a disc of conductive material (usually copper or aluminum) in a magnetic field. As the disc rotates, the magnetic field induces a current in the disc, creating an electrical potential difference between the center and the outer edge of the disc.

3. What is the purpose of a Faraday generator?

The primary purpose of a Faraday generator is to generate electricity. It can be used in various applications, such as power generation in hydroelectric dams, wind turbines, and even bicycles.

4. Can a Faraday generator work without a magnetic field?

No, a Faraday generator requires a magnetic field in order to work. Without a magnetic field, there would be no induction of current in the disc and thus no conversion of mechanical energy into electrical energy.

5. Are there any limitations to a Faraday generator?

Like any other device, a Faraday generator has its limitations. It can only generate electricity when the disc is rotating at a constant speed, and the strength of the magnetic field also affects its efficiency. Additionally, the efficiency of a Faraday generator decreases with increasing frequency of rotation.

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