# How does the magnetic field creates the potential difference ?

#### usmansa1

Joined Jan 22, 2017
40
Hi,

I was reading electricity and found that the difference in potential of both end is the difference in the quantity of the charges on the both ends (More positive charge and less positive charge or vice versa). In the mechanism of generation of electricity a metal coil is rotated in magnetic field and current is generated due to variation in the magnetic field. What I dont understand that how does the difference in potential will create this difference in charges ?

#### Papabravo

Joined Feb 24, 2006
21,228
Charges moving in a magnetic field are subject to a force that moves them. When charges move, potential differences are created. It is a consequence of Maxwell's equations that a changing magnetic field produces an electric field, AND a changing electric field produces a magnetic field. Everything is coupled when there is motion.

#### crutschow

Joined Mar 14, 2008
34,468
Simplistically you can think of it as the moving magnetic field dragging the electrons along with it.

Joined Jul 18, 2013
28,700
Also see Flemings right hand rule.
Max.

#### nsaspook

Joined Aug 27, 2009
13,315
Hi,

I was reading electricity and found that the difference in potential of both end is the difference in the quantity of the charges on the both ends (More positive charge and less positive charge or vice versa). In the mechanism of generation of electricity a metal coil is rotated in magnetic field and current is generated due to variation in the magnetic field. What I dont understand that how does the difference in potential will create this difference in charges ?
No sure what you are asking.
Motional Emf? Energy is transferred (KE) from the physical rotation/movement of charges in the metal coil into electrical energy by the Lorentz force.

Try reviewing this series first:

#### slackguy

Joined Feb 11, 2016
76
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#### crutschow

Joined Mar 14, 2008
34,468
In the mechanism of generation of electricity a metal coil is rotated in magnetic field and current is generated due to variation in the magnetic field.
Most practical alternators rotate the magnetic field, which generates the voltage in the fixed stator coil wires.

#### BobaMosfet

Joined Jul 1, 2009
2,113
Hi,

I was reading electricity and found that the difference in potential of both end is the difference in the quantity of the charges on the both ends (More positive charge and less positive charge or vice versa). In the mechanism of generation of electricity a metal coil is rotated in magnetic field and current is generated due to variation in the magnetic field. What I dont understand that how does the difference in potential will create this difference in charges ?
A difference in potential doesn't create a difference in charges, it _is_ a difference in charges. And as you know, like charges repel, so there you go. You got movement.

#### slackguy

Joined Feb 11, 2016
76
A difference in potential doesn't create a difference in charges, it _is_ a difference in charges. And as you know, like charges repel, so there you go. You got movement.
in the situation your are asking, the change in magnetic flux equal current (with the right constants and equation used of course)

if the magnetic field does not change, the potential differences does not

obviously, if there is zero potential difference than there is nothing in the magentic field

it's very difficult to build your own coil btw - doing so will result in a very low efficiency device. if you need one, buy one.

Correct. U means potential energy (measured in Joules), the same energy measurement used for heat, work, flow, sound waves, light waves - all when using the right constants are equatable.

Ud, potential difference means a charge in a field THAT HAS MOVED (like the difference in potential from 1lb at 10' and 1lb at 5') (noting neither is necessarily on the ground: it means difference only)

Up, potential at a point means the value of moving that charge away from the electric field off to infinity

U is called V, for Mr. Voltir in electronics: but it's the energy remaining for a particle in an inverse square vector field all the same.

The universe "conserves energy" - something at rest (or in motion without friction) stays that way unless moved by some force. An electron will not move unless there is external influence. Electric fields (like charges repel) is one influence. Another is magnetism.

Magnetism is strange, it's taught as a field of electrons spinning on their own axis. Think of of rolling a ball slowly into a ball that's spinning fast. I avoid the issue of the slow ball taking a spin in result, spin being required to be accelerating (not chaning speed), distance between, other strange re-induced effects, and say simply: the electron moves to avoid change in it's own potential energy level to a place where the least energy is gained - gaining a spin is gaining energy, and linear motion is how the electron "conserves energy" to (mostly) evade getting spun. Let's stop here. But quantum mechanics, in making a chart of electron configuration in elements, counts spin (which should convince you that you math will be needed).

my top 4 statements were the ones most practical for "all about circuits"

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#### slackguy

Joined Feb 11, 2016
76
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#### slackguy

Joined Feb 11, 2016
76
.

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#### bogosort

Joined Sep 24, 2011
696
It's a strange concept but that's because magnetism is a strange thing.
It's strange only when we try to pigeonhole the electric field and the magnetic field as different things. Granted, it can be computationally convenient to pretend that they're different, but the didactic mystery disappears once we realize there are no preferred frames of reference. This has the subtle but profound implication that magnetism is just a relativistic effect, the electric equivalent of the Coriolis effect. If I am stationary with respect to a moving charge, I will measure a magnetic field; however, if you are comoving with the very same charge, you will measure an electrostatic field and no magnetic field. Same charge, two different interpretations of the physics. Our worldview is broken unless we realize that the electric field and the magnetic field are one and the same thing, the electromagnetic field.

#### cmartinez

Joined Jan 17, 2007
8,257
magnetism is just a relativistic effect, the electric equivalent of the Coriolis effect
Interesting idea, would you mind elaborating?

#### nsaspook

Joined Aug 27, 2009
13,315
After a few introductory comments and disclaimers, I'll review Purcell's ideas and thus try to convince you to try this approach yourselves. The two ideas are first, that magnetism is a consequence of length contraction, and second, that electromagnetic radiation happens because of the cosmic speed limit, that is, because information can't travel faster than the speed of light.
https://en.wikipedia.org/wiki/Electromagnetic_tensor
https://en.wikipedia.org/wiki/Electromagnetic_four-potential

A analogy to the electromagnetic tensor field would be a 3D cylinder projected into 2D space. As we change the frame of reference in our 2D space, it changes from a circular object to a rectangular object while the physical 3D entity remains the same.

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#### bogosort

Joined Sep 24, 2011
696
Interesting idea, would you mind elaborating?
The magnetic field is like the Coriolis effect in the sense that one can always choose coordinates that make either disappear. In other words, the magnetic force -- like the Coriolis force or the centrifugal force -- is a fictitious force that we introduce in certain reference frames to explain the apparent motion of objects that would not otherwise occur (with respect to some other reference frame).

Feynman (as usual) says it best:
http://www.feynmanlectures.caltech.edu/II_01.html

See section 1-5 (What are the fields?).