Magnetic Field and Work

In summary, the conversation discusses the relationship between a magnetic field and the work it can do on electrons in a wire. It is mentioned that magnetic forces do not do work, but a time-varying magnetic field can lead to an electric field that does work. Faraday's law is brought up, both in integral and differential form, and its application in this scenario is discussed. The concept of a field that does not act at a distance is also mentioned, along with the idea of a locally acting 4-vector potential and its impact on free electrons in a conductor.
  • #1
Phrak
4,267
6
How does a magnetic field do work on the electrons in a wire?

If F = q v x B, the magnetic field is always perpendicular to the velocity of the free charge. After a small time interval, dx = v dt, so that v and x are in the same direction.

For the magnetic field to do work on the charge, dW = F dot dx. But F and dx are perpendicular, aren't they?, so no work seems to be done.
 
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  • #2
That's right. Magnetic forces never do any work.
 
  • #3
A time varying magnetic field will lead to an electric field that does work.
An example is Faraday's law.
 
  • #4
An electric generator does work because the field changes?
 
  • #5
nicksauce said:
That's right. Magnetic forces never do any work.
A magnetic field acting on a permanent or electric magnetic can do work.
 
  • #6
Phrak said:
An electric generator does work because the field changes?
That is how an induction motor works.
Other motors use a permanent or electric magnet as an armature,
and a magnetic field does do work on the armature.
 
  • #7
Pam, thank you for answering.

You threw me so far. I am now sure you are applying Faraday's law in integral form,
[tex]\int _{_\partial S} \overline{E} ds = -\int _{S} \partial_{t}\overline{B}dxdy[/tex] ,
it must surely be.

This makes some very good sense.

I could not possibly see how to apply Faraday's law in differential form,

[tex]\nabla\times \overline{E} = -\partial_{t}\overline{B}[/tex].

Unfortunately, I still cannot.

In the vicinity of the wire B is unchanging, we should presume. In such a manner [tex]\partial_{t}\overline{B}[/tex] should be zero as well, in this locally manner. But should this not make [tex]\nabla \times \overline{E}[/tex] zero as well?

Something I am missing.
 
  • #8
Can this be understood in terms of a field that doesn't act at a distance?

Does a locally acting 4-vector potential, A and Dirac's equation of A acting on the phase of the free electrons in a conductor make some sense of it?
 

What is a magnetic field?

A magnetic field is a region in space where a magnetic force can be detected. It is created by moving electric charges, such as electrons, and is characterized by its direction and strength.

How is a magnetic field created?

A magnetic field is created by the movement of electric charges, such as electrons. This can occur in a variety of ways, including the flow of current through a wire or the movement of charged particles in the Earth's core.

How does a magnetic field affect objects?

A magnetic field can exert a force on objects that have a magnetic property, such as iron or other metals. This force can attract or repel the object, depending on the direction of the magnetic field.

What is the relationship between magnetic field and work?

The work done by a magnetic field on an object is equal to the force exerted by the field multiplied by the distance the object moves in the direction of the force. In other words, the magnetic field can do work on an object by exerting a force and causing it to move.

How do scientists measure magnetic fields?

Scientists use a device called a magnetometer to measure the strength and direction of a magnetic field. This can be done using a variety of techniques, such as using a compass or a device that detects the magnetic force on a moving charged particle.

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