What Causes Rotation in a Non-Rotating Magnet?

  • Thread starter MS La Moreaux
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In summary: Hassan2,In the linear case, the disk would start off rotating because the voltage would be constant and would cause the electrons to move. But in the case of the N machine, the voltage would go up and down as the disk rotated and this would not cause the electrons to move.
  • #1
MS La Moreaux
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2
If a permanent magnet is moved in a direction at right angles to the magnet field lines in the magnet, is an emf produced across the magnet?

Mike
 
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  • #2
If you mean it is moving in an external field, yes it is induced, just like in a piece of Iron. But if you mean there is no field except for the magnets own field, then in classical electromagnetic no emf is induced because the relative motion of the magnet and its velocity is zero. I don't know what happens whenthe velocity approaches the speed of light.
 
  • #3
Hassan2,

It seems to be the case that a magnet's field is not attached to the magnet. If an electrically conductive disk magnet (with the faces the poles) rotates like a wheel, an emf is developed from the center to the rim. This is a type of homopolar generator known as a DePalma N Machine. My question relates to the linear version of it.

Mike
 
  • #4
If you think the problem is interesting, can you please make a simple drawing of it?
 
  • #5
Rotational motion and translation motion are different things. If you translate an object (move it in a straight line at a constant speed) then the object it still in an inertial frame and therefore acts (to itself) as if it were at rest. A translating object does not create an EMF in its frame of reference because it is not moving in its frame a reference. A rotating frame, on the other hand, is not inertial and so you cannot put yourself in a rotating object's rest frame and apply the standard equations. Homopolar generators work because the motion is rotational.
 
  • #6
Hassan2,

Sorry, but I do not know how to add a drawing.
 
  • #7
crisbaird,

I am having trouble understanding this. If the N machine is operated as a motor, it will start from a stationary position. Therefore, at the instant of starting, there is no rotary motion and everything is in the same frame of reference.
 
  • #8
MS La Moreaux said:
crisbaird,

I am having trouble understanding this. If the N machine is operated as a motor, it will start from a stationary position. Therefore, at the instant of starting, there is no rotary motion and everything is in the same frame of reference.

And that is why at the instant of starting, there is no EMF
 
  • #9
Yes, but what causes the disk to rotate? It would seem that the conduction electrons in the disk have a force exerted on them by the magnetic field of the disk even though there is no rotation at the start. How does this differ from the linear version of the motor? Why would there not be movement of the magnet in the linear case?
 

1. What is motional induction?

Motional induction is a phenomenon that occurs when a conductor moving through a magnetic field or a changing magnetic field induces an electromotive force (EMF) or voltage in the conductor. This is based on Faraday's law of induction which states that a changing magnetic field can induce an electric current in a conductor.

2. How does motional induction work?

Motional induction works by the interaction between a magnetic field and a moving conductor. As the conductor moves through the magnetic field or the magnetic field changes, the lines of magnetic flux cut through the conductor, creating a change in the magnetic flux. This change in flux induces an EMF in the conductor, which can then drive an electric current.

3. What are some real-life applications of motional induction?

Motional induction has many practical applications, such as in generators, motors, and transformers. Generators use motional induction to convert mechanical energy into electrical energy, while motors use it to convert electrical energy into mechanical energy. Transformers use motional induction to transfer electrical energy from one circuit to another.

4. Can motional induction be used to generate electricity?

Yes, motional induction is a key principle in generators, which are used to generate electricity. As a conductor is rotated in a magnetic field, the changing magnetic flux induces an EMF in the conductor, which can then drive an electric current. This process is used in power plants to generate electricity for our homes and businesses.

5. What factors affect the amount of EMF induced in a conductor?

The amount of EMF induced in a conductor depends on several factors, including the strength of the magnetic field, the speed of the conductor, and the length of the conductor. The angle between the magnetic field and the direction of motion of the conductor also plays a role. Generally, a stronger magnetic field, higher speed, and longer conductor will result in a higher induced EMF.

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