How does a moving magnet induce a current in a coil?

  • Thread starter ylem
  • Start date
  • Tags
    Current
In summary, the conversation discusses the confusion of understanding how an induced current is created in a Physics experiment involving a coil and a magnet. It is suggested to look at the Faraday-Maxwell's law and consider the effects of an unsteady magnetic field and the movement of a conductor. The concept of a frame of reference is also mentioned. The conversation ends with a question about the physical significance of the gradient and area under the curve in the graph of voltage against time.
  • #1
ylem
32
1
Hello!

I've just realized, when trying to do a write up for a Physics experiment (about a coil and a magnet) that I don't know how you get an induced current!

What's actually going on when the magnet moves through the coil? What are the electrons doing to induce a current?

I'm totally confused and my Physics textbook is not helping at all!

Please help!
 
Physics news on Phys.org
  • #2
Take a look at the Faraday-Maxwell's law:

[tex] \epsilon=\oint\overline{E}\cdot\overline{dl}=-\int\int\frac{\partial \overline{B}}{\partial t}\cdot \overline{dS}+\oint(\overline{v}\times\overline{B})\cdot \overline{dl}[/tex]

A FEM can be induced by two effects:

-An unsteady magnetic field inside a steady electric closed circuit.
-The movement of a conductor inside a magnetic field.

In your example, you are causing a [tex] \frac{\partial \overline{B}}{\partial t}[/tex] moving the magnet inside a cylindrical-shaped coil of section S. The FEM is induced internally in the conductor displacing the electrons towards one of the extremes, and positive charges to the other. The vehicle of transmision is a bit heuristic for me, so that maybe a physicist could help you very much.
 
Last edited:
  • #3
It might help to think about how things look in a frame of reference moving with the magnet. There the magnetic field is static and the charges in the coil are moving through that static field. They will be subjected to the [itex]\vec v \times \vec B[/itex] force and respond to it. In the coil frame, that response is said to be due to the induced EMF.
 
  • #4
A nice change of reference frame, Tide. Sorry for writting upside down the letters FEM and EMF.

FEM=Fuerza ElectroMagnética (spanish)
EMF=ElectroMagnetic Force (english)

It's an usual error in my spelling to think of my native language... :frown:
 
  • #5
Clausius,

Gracias!

I knew what you meant by FEM and I was by no means attempting to correct you! Everyone working in the sciences is aware of the linguistic differences used in writing abbreviations.
 
  • #6
Thanks everyone! It all makes sense now!

I have another question though! The graph of voltage against time: what physical significance is the gradient and the area under the curve?
 

1. How do you induce a current?

Inducing a current involves creating a changing magnetic field around a conductor, which then produces a flow of electrons or current in the conductor. This can be achieved through various methods such as moving a magnet near a coil of wire, changing the orientation of a coil in a magnetic field, or using electromagnetic induction.

2. What is electromagnetic induction?

Electromagnetic induction is the process of creating a current in a conductor by moving the conductor through a magnetic field or by changing the magnetic field around the conductor. This is based on Faraday's Law, which states that a changing magnetic field will induce a current in a conductor.

3. What materials can be used to induce a current?

Any material that is a good conductor of electricity can be used to induce a current. This includes metals such as copper, silver, and gold, as well as some non-metals like graphite. The key is to have a material that allows for the flow of electrons.

4. How does the strength of the magnetic field affect the induced current?

The strength of the magnetic field directly affects the induced current. A stronger magnetic field will induce a greater current in a conductor, while a weaker magnetic field will induce a smaller current. This is because a stronger magnetic field will cause a greater number of electrons to move, resulting in a larger current.

5. Are there any practical applications for induced current?

Yes, there are many practical applications for induced current. Some examples include generators, transformers, and electric motors. These devices use electromagnetic induction to convert mechanical energy into electrical energy or vice versa. Induced current is also used in wireless charging technology and some medical devices.

Similar threads

B Understanding magnetic flux change during the falling of magnet
    • Electromagnetism
Replies
1
Views
339
Induced current in a coil from a constant uniform magnetic field?
    • Electromagnetism
Replies
5
Views
868
I Quantifying the magnetic force on a magnet moving through a coil?
    • Electromagnetism
Replies
5
Views
1K
I Which law defines the AC inducing voltage in the inductor?
    • Electromagnetism
Replies
25
Views
1K
I Mutual inductance in a transformer
    • Electromagnetism
Replies
16
Views
1K
B Confusing diagram of a rotating coil in a magnetic field
    • Electromagnetism
Replies
4
Views
967
I Induced electric fields and induced magnetic fields confusion
    • Electromagnetism
Replies
9
Views
1K
Lenz's law and instantaneous change in inductor's current
    • Electromagnetism
Replies
3
Views
978
How Does Magnetic Force Affect a Falling Coil's Velocity and Kinetic Energy?
    • Electromagnetism
Replies
10
Views
1K
I Hall effect -- is it always applicable?
    • Electromagnetism
Replies
7
Views
949

Hot Threads

Recent Insights

Back
Top