Static free charge in a time varying infinite uniform magnetic field

In summary, the conversation discusses the visualization of the electric field generated by a time-varying magnetic field according to Maxwell's equations. It also raises the question of the trajectory of a static free charge in this field and the physical viability of the situation. The issue of a uniform magnetic field is also addressed and the suggestion is made to start from a true solution of Maxwell's equations, such as a standing wave in a cavity.
  • #1
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Hello,

Let's imagine we have an infinite plane (or large enough compared to the region of interest and measurements) pierced in normal direction by magnetic field B which is uniformly distributed but time varying. For the sake of simplicity we'll presume the magnetic induction is linearly (and perpetually) changing in time.

According to Maxwell equations that would generate a "curly" electric field with constant curl vector:

×E = -∂B(t)/∂t=const

The question is how can one visualize the actual vector field of E (the solution for E). Are there infinite number of solutions?
The traditional way of visualizing electric field lines curling around the magnetic field lines seems to fail in this case (which B lines should the E lines wrap around?).

And the consequence question - if we place a static free charge in the field described - how will it start moving (in what direction), what would be it's trajectory having in mind that once accelerated by the E field it will start being affected by the B field (I assume Lorentz low would account completely for both the effects).
 
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  • #2
I am not sure you have desribed a physically viable situation. Uniform magnetic field will have no divergence and no curl. By Helmholtz decomposition such field is zero
(https://en.wikipedia.org/wiki/Helmholtz_decomposition).

We can assume that magnetic field is nearly constant with slight decay away from the centre. This gives you nonzero curl of magnetic field, and therefore non-zero first derivative of electic field (since ##\boldsymbol{\nabla}\times\mathbf{B}=c^2\mathbf{\dot{E}}##), but then electric field must be at least quadratic in time.

This however creates a problem since ##\boldsymbol{\nabla}\times\mathbf{E}=-\dot{B}\mathbf{\hat{z}}##, and you said that magnetic field is linear in time (so its derivative with respect to time cannot be quadratic in time).

Of course it is possible to create a region of nearly uniform magnetic field that is changing in time. However, I suggest you get there by starting from a true solution of Maxwells equations. For example a standing wave in the cavity will give you a region of nearly uniform oscillating magnetic field (which will be roughly linear in time for a short period).
 
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1. What is static free charge?

Static free charge refers to a type of electric charge that does not produce any electric fields or currents. This means that the charge is not moving and is in a state of equilibrium.

2. What is a time varying infinite uniform magnetic field?

A time varying infinite uniform magnetic field is a magnetic field that has a constant strength and direction throughout all of space and is changing over time.

3. How does a time varying infinite uniform magnetic field affect static free charge?

The presence of a time varying infinite uniform magnetic field does not affect static free charge since the charge is not moving and therefore not affected by the magnetic field.

4. Can a time varying infinite uniform magnetic field create static free charge?

No, a magnetic field alone cannot create static free charge. Static free charge can only be created through the transfer of electrons or other charged particles.

5. What are the practical applications of studying static free charge in a time varying infinite uniform magnetic field?

Studying static free charge in a time varying infinite uniform magnetic field can help us understand the fundamental principles of electromagnetism and can also have practical applications in fields such as electrical engineering and physics research.

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