Why does a change of magnetic flux induce an EMF?

• funmi
In summary, he explains that a changing magnetic flux induces an emf because it allows you to do work with it, and that you never get something for nothing so you don't get emf from a static magnetic field.
funmi
How and why does a changing magnetic flux induce an emf? Why doesn't a static one also produce one? How are the electric and magnetic forces related? Why do you move a wire through a magnetic field so that the wire, the motion, and the magnetic field are all mutually orthogonal in order to produce the emf? I want an intuitive explanation please. Also take into consideration that I'm a high school student.

Last edited:
This is going to be a very difficult question to answer. “Why” questions are notoriously difficult to answer. Basically, to answer a “why” question requires that the questioner and the answerer have an agreed upon set of accepted assumptions or background that can be used as explanations.

Unfortunately, you exclude math (not intuitive), explanations by contradiction, and any concepts introduced after high school. I have no idea what explanations are left, what common basis of understanding you will allow. Since you have a priori rejected so much of our usual possible common basis, please spend some time explaining what we can use in an acceptable answer.

DaveE
Dale said:
This is going to be a very difficult question to answer. “Why” questions are notoriously difficult to answer. Basically, to answer a “why” question requires that the questioner and the answerer have an agreed upon set of accepted assumptions or background that can be used as explanations.

Unfortunately, you exclude math (not intuitive), explanations by contradiction, and any concepts introduced after high school. I have no idea what explanations are left, what common basis of understanding you will allow. Since you have a priori rejected so much of our usual possible common basis, please spend some time explaining what we can use in an acceptable answer.
Please explain as simply as you can, if you reference something I don't understand I'll ask for clarification

funmi said:
Please explain as simply as you can, if you reference something I don't understand I'll ask for clarification
If you accept the potential formulation of Maxwell’s equations then Faraday’s law is a vector identity.

If you accept the conservation of magnetic flux then Faraday’s law can be derived using differential forms.

If you accept Coulomb’s law and relativity then Faraday’s law can be derived using tensors.

etotheipi and berkeman
funmi said:
How and why does a changing magnetic flux induce an emf? Why doesn't a static one also produce one?
How's this: with an emf or voltage, you can do work (run a motor, or heat a resistor, etc.), right? If you could do that with a static field, you would be getting something for nothing. You never get something for nothing, so you don't get emf from a static magnetic field.

gmax137 said:
How's this: with an emf or voltage, you can do work (run a motor, or heat a resistor, etc.), right? If you could do that with a static field, you would be getting something for nothing. You never get something for nothing, so you don't get emf from a static magnetic field.
Earlier he had a priori rejected any “if not then this would happen” explanations, but he appears to have changed his mind. So maybe this will satisfy him now.

I think the best answer is that that appears to be the way the laws of physics are. I'm not sure we know "why", although we can make other related observations and fit them all into a fairly simple and consistent set of laws that allow us to predict how nature works.

Watch this clip of one of the greatest intellects of the 20th century answer your question:

Dale
DaveE said:
Watch this clip of one of the greatest intellects of the 20th century answer your question.

Came to find out about magnets, ended up learning why Aunt Minnie slipped on the ice. Joking aside, a pretty enlightening video.

1. What is magnetic flux?

Magnetic flux is a measure of the amount of magnetic field passing through a given area. It is represented by the symbol Φ and is measured in units of webers (Wb).

2. How does a change in magnetic flux induce an EMF?

When there is a change in the magnetic field passing through a conductor, it creates an electric field in the conductor. This electric field then causes a flow of electrons, resulting in an induced electromotive force (EMF).

3. What factors affect the magnitude of the induced EMF?

The magnitude of the induced EMF depends on the rate of change of the magnetic flux, the number of turns in the conductor, and the strength of the magnetic field.

4. What is Lenz's law and how does it relate to Faraday's law of induction?

Lenz's law states that the direction of the induced EMF will always be such that it opposes the change in magnetic flux that caused it. This is in accordance with Faraday's law of induction, which states that the magnitude of the induced EMF is directly proportional to the rate of change of the magnetic flux.

5. What are some practical applications of electromagnetic induction?

Electromagnetic induction has numerous practical applications, including power generation in generators, transformers, and electric motors. It is also used in devices such as induction cooktops, metal detectors, and magnetic levitation trains.

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