# Explanation of Electromagnetic Induction

1. Apr 19, 2012

### Thundagere

I took a physics competition recently and found I missed 6 questions on electromagnetic induction and the like. I've always been shaky here, so I'm wondering if anyone can give me an online resource, or just explain to me exactly how it works (i.e., Lenz's law, etc., etc.)? I'm sorry for not having anything more detailed, but the fact is I'm missing the entire concept as it is.

2. Apr 19, 2012

### BruceW

Faraday's law of induction is the important equation to calculate the induced emf. In words, the induced emf is equal to the negative of the rate of change of magnetic flux with time. Lenz's law is an explanation for why the negative sign must be there - because the induced emf always causes currents to flow which reduce the rate of change of magnetic flux with time. If the negative sign was not there, currents would flow which cause a greater emf, which further cause greater currents, creating a big problem.

3. Apr 19, 2012

### Thundagere

This big problem is violation of conservation of energy, right?
Why is it that induction occurs in the first place? Is it because of the electric field's affect on the electrons in a magnet?

4. Apr 22, 2012

### BruceW

yep, the negative sign is a good example of energy conservation, because it means that it requires energy to cause induction.
I'm not sure what you mean by this. What experiment set-up are you imagining here?

5. Apr 22, 2012

### Staff: Mentor

You're basically asking, why are Maxwell's equations (of which Faraday's Law is one) are true? This is like asking, why are Newton's laws of motion the way they are?

This is in the context of classical physics. In quantum field theory we can say that electromagnetism is due to the local U(1) gauge symmetry of the universe, but I suspect that might not help you very much. Besides, it begs the question, why does the universe have local U(1) gauge symmetry? :uhh: