# Displacement current vs eddy current

## Main Question or Discussion Point

Hello,
I'm new on this forum. I hope I could help some of you next days. But today I have a question for you.
I have a geophysics oral exam on wednesday.
The course material is not clear, and I don't understand the wikipedia pages.

What is the physical difference between displacement current and eddy current ?
I know that eddy currents can be induced in the ground under the effect of primary magnetic field. Then, they create secondary magnetic fields.

But I don't get the meaning of displacement current. I thought displacement currents were explained by polarized grains in the ground. Due to magnetic and electric variations charged particules move within the ground. These movements induce displacement currents.
Is that right ?

So the difference would be that eddy current is not due to particule movement but displacement current is ?
By the way is induced polarization and displcement effect the same physical phenomen ?

Thanks a lot for you help.
V

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Displacement current is actually a misnomer. Displacement currents aren't actual currents. They are merely a mathematical tool to understand what is going on when the electric field changes. As Maxwell found out, when there are changes in the electric field, the magnetic field also changes in a way that could be explained if we assumed there were electric currents, called displacement currents. But there's no movement of charges (displacement currents may happen even in vacuum), so they aren't really a current.

Eddy currents, on the other hand, are real currents. They occur when the magnetic field changes (notice that displacement currents are the result of changes in the electric field). In an eddy current, charges move around in a material, so it is a current.

Take a look at http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/ . On Lecture 19, he gives the best explanation of what a displacement current is.

Thanks a lot. I m going to read your post and watch the video carrefully.

you said you have an oral exam of geophysics , so what kind of your study, geophysics or geology, Waiting for your kindly reply.

I'm studying GIS for environmental purposes. But that's more about geophysics than geology, despite it's not really geophysics.
Thanks "Acut" I got a nice grade for my oral exam.

I'm studying GIS for environmental purposes. But that's more about geophysics than geology, despite it's not really geophysics.
Thanks "Acut" I got a nice grade for my oral exam.
You're welcome! I'm glad that information helped!