Question about electromagnetism

In summary, the conversation discusses the relationship between the movement of a magnet and the flow of electrons in a conductor. The participants mention the third Maxwell relation, which uses Stokes theorem to explain the integral form. They also discuss how a permanent magnet can induce an electromotive force and drive electrons through a wire. The direction of the current is determined by the direction of the fingers curling around the coil. The participants also mention the Lorentz force and recommend studying physics textbooks for a better understanding. The conversation ends with a question about the direction of electrons and a suggestion to study Maxwell's equations for the answer.
  • #1
scientist91
133
0
I have one question. It is about current in conductor. It is about electromagnet induction. So I move the magnet among conductor in closed circular loop, like on this http://www.imagehosting.com/show.php/710601_untitled5.bmp.html"
So is the way of moving of the electrons depends from the way of the moving magnet?
Let's say I move the magnet in direction of the arrow (like on the pic), so the electrons will move in the direction of the arrow (like on the picture), right? Thank you.
 
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  • #2
hi!

there's the third maxwell relation: curl E == -d/dt(B).
You than use stokes theorem to get its integral form:
int[E*dl](contour)==int[-d/dt(B)](surface, enclosed by contour).
So, you have your permanent magnet, it's like a manetic dipole. Its magnetic field attenuates like 1/r^3. So you pick a turn in your coil, and move your dipole into it. Than you're integrating the magnetic flux density(B) on the surface, enclosed by the wire(the one turn in the coil), and you get an electromive force, that drives electrons through the wire, like a voltage applied on some other wire, according to Ohm's law.

So as you can see, bringing the dipole closer to the loop, B is rising, than as you left the center of the loop, the B is getting weaker. So first you get a current flowing one direction, and than in the opposite direction. Than you can generalize, and take the whole coil into consideration.
 
  • #3
mcstar said:
hi!

there's the third maxwell relation: curl E == -d/dt(B).
You than use stokes theorem to get its integral form:
int[E*dl](contour)==int[-d/dt(B)](surface, enclosed by contour).
So, you have your permanent magnet, it's like a manetic dipole. Its magnetic field attenuates like 1/r^3. So you pick a turn in your coil, and move your dipole into it. Than you're integrating the magnetic flux density(B) on the surface, enclosed by the wire(the one turn in the coil), and you get an electromive force, that drives electrons through the wire, like a voltage applied on some other wire, according to Ohm's law.

So as you can see, bringing the dipole closer to the loop, B is rising, than as you left the center of the loop, the B is getting weaker. So first you get a current flowing one direction, and than in the opposite direction. Than you can generalize, and take the whole coil into consideration.
So when I move the magnet it is possible that the electrons will move on any direction right?
 
  • #4
no, not any direction. either direction is correct.
you grab the coil with you right hand, and in the direction, your fingers curl, will the current flow, when you pull out the dipole, so the loop experiences weaker and weaker B-field. when you mive the dipole in, the opposite is true.
 
  • #5
mcstar said:
no, not any direction. either direction is correct.
you grab the coil with you right hand, and in the direction, your fingers curl, will the current flow, when you pull out the dipole, so the loop experiences weaker and weaker B-field. when you mive the dipole in, the opposite is true.
do the electrons move from the stronger B field to the weaker B field?
 
  • #6
you don't seem to understand the whole idea.
the electrons doesn't move because of the B field. they move, because a time-dependent magnetic field is present in the loop, and it induces an electric field, which is not curl-free. this field drives the electrons.
magnetic fields exert a force on charges, its the Lorentz-force:
F=q*v x B, where x is the cross product of the velocity of the electron and the magnetic flux density vector.

however i strongly recommend you to grab some physics textbooks, and read them carefully, these things must be in them, and probably they can teach you better than me.
 
  • #7
mcstar said:
you don't seem to understand the whole idea.
the electrons doesn't move because of the B field. they move, because a time-dependent magnetic field is present in the loop, and it induces an electric field, which is not curl-free. this field drives the electrons.
magnetic fields exert a force on charges, its the Lorentz-force:
F=q*v x B, where x is the cross product of the velocity of the electron and the magnetic flux density vector.

however i strongly recommend you to grab some physics textbooks, and read them carefully, these things must be in them, and probably they can teach you better than me.

I know all of that things. But my question is that the electrons go from anode to cathode. So there are two direction that can electrons move. From the right and the left, can they move (the electrons) in opposite directions?
 
  • #8
mcstar said:
no, not any direction. either direction is correct.
you grab the coil with you right hand, and in the direction, your fingers curl, will the current flow, when you pull out the dipole, so the loop experiences weaker and weaker B-field. when you mive the dipole in, the opposite is true.

i already wrote the answer.
 
  • #9
mcstar said:
i already wrote the answer.
can you draw some picture please (because of my bad english)? Thank you very much.
 
  • #10
I know all of that things. But my question is that the electrons go from anode to cathode.
I don't think you know anything. Did you understand posts #2 and #6 ?

Electrons go from cathode to anode. There's no cathode or anode in your setup. As has been told to you in all your threads - the answer is in Maxwell's equations. Go away and study them.
 
  • #11
Mentz114 said:
I don't think you know anything. Did you understand posts #2 and #6 ?

Electrons go from cathode to anode. There's no cathode or anode in your setup. As has been told to you in all your threads - the answer is in Maxwell's equations. Go away and study them.
Is the magnetic field different, of the both of the cases?
 
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  • #12
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What is electromagnetism?

Electromagnetism is the physics of the electromagnetic field, which is a type of energy that includes both electric and magnetic components. It is responsible for the behavior of electrically charged particles and plays a crucial role in many natural phenomena and technological applications.

What is the difference between electricity and magnetism?

Electricity and magnetism are two distinct but related concepts. Electricity refers to the flow of electric charge, while magnetism is the force that results from the movement of electric charges. In other words, electricity is the cause of magnetism, and magnetism is the effect of electricity.

How does electromagnetism work?

Electromagnetism works by the interaction between electric and magnetic fields. When an electric current flows through a wire, it creates a magnetic field around the wire. This magnetic field can then interact with other magnetic fields to produce forces and motion.

What are some practical applications of electromagnetism?

Electromagnetism has numerous practical applications, such as in motors and generators, which use the interaction between electric and magnetic fields to produce mechanical motion. It is also used in various electronic devices, including televisions, computers, and cell phones. Electromagnetism is also essential in medical imaging, such as MRI machines, which use magnetic fields to produce images of the body's internal structures.

What is the relationship between electromagnetism and light?

Electromagnetism and light are closely related. Light is a form of electromagnetic radiation, which means it is made up of both electric and magnetic fields. The speed of light is also a fundamental constant in electromagnetism, and many of the principles and equations used to describe electromagnetic phenomena also apply to light.

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