Displacement current vs eddy current

In summary, the conversation discusses the difference between displacement current and eddy current in geophysics. Displacement current is not an actual current but a mathematical tool to understand changes in the electric field, while eddy current is a real current that occurs when the magnetic field changes. The conversation also mentions a helpful video lecture on the topic and briefly touches on the speaker's studies in GIS for environmental purposes.
  • #1
VaikGeomatics
3
0
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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  • #2
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.
 
  • #3
Thanks a lot. I m going to read your post and watch the video carrefully.
 
  • #4
you said you have an oral exam of geophysics , so what kind of your study, geophysics or geology, Waiting for your kindly reply.
 
  • #5
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.
 
  • #6
VaikGeomatics said:
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!
 

1. What is the difference between displacement current and eddy current?

Displacement current is a phenomenon that occurs in an electric field when there is a change in the electric flux through a surface. It is a type of electric current that is not caused by the movement of electrons, but rather by the changing electric field. On the other hand, eddy current is a type of electric current that is induced in a conductor when it is exposed to a changing magnetic field.

2. How are displacement current and eddy current related?

Displacement current and eddy current are both types of electric currents that are induced by changing electric or magnetic fields. However, they differ in their causes and effects. Displacement current is caused by a changing electric field, while eddy current is caused by a changing magnetic field. Additionally, displacement current is typically considered to be a displacement of electric charge, while eddy current is a circulation of electric charge.

3. What are some practical applications of displacement current and eddy current?

Displacement current is used in various electrical devices, such as capacitors and transformers. It also plays a role in the propagation of electromagnetic waves. Eddy current, on the other hand, is commonly used in non-destructive testing to detect defects in metal objects. It is also utilized in induction heating for melting metals and in magnetic braking for slowing down vehicles.

4. How do displacement current and eddy current affect each other?

Displacement current and eddy current can interact with each other in some situations. For example, in a transformer, displacement current flows through the insulating material between the transformer's coils, while eddy currents are induced in the transformer's metal core. These eddy currents can lead to energy loss and heating. In some cases, eddy currents can also produce a magnetic field that affects the displacement current.

5. Can displacement current and eddy current be controlled or minimized?

Yes, displacement current and eddy current can be controlled or minimized in certain applications. For example, in transformers, the use of laminated cores can reduce eddy currents and energy loss. In electrical motors, the use of segmented rotor cores can reduce eddy currents. Additionally, proper design and material selection can help minimize the effects of displacement current and eddy current in various applications.

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