- #1
girts
- 185
- 22
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.
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.