# B Electromagnetic induction question, coils and magnets

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1. Jun 1, 2016

### Hannah7h

Say you have a coil connected in a closed circuit. You then move a magnet inside of the coil and it remains stationary inside of the coil. Is the magnet, even though it is stationary, still inducing an emf in the coil or is it not? I'm guessing it doesn't induce an emf in the coil because there is no change in flux linkage, but I'm not too sure.

Thank you for any help

2. Jun 1, 2016

### Staff: Mentor

I am not sure what you are asking. How can the magnet both move and remain stationary?

Do you mean that both the magnet and the coil are moving at the same velocity so that they have no relative motion? Or do you mean that the magnet remains at rest and the coil moves relative to the magnet?

3. Jun 1, 2016

### Hannah7h

Oh sorry! I meant you move the magnet INTO the coil and then it remains stationary inside of the coil

4. Jun 1, 2016

### Drakkith

Staff Emeritus
That's correct. Since the magnetic field through the coil's windings isn't changing, there is no induced emf in the coil.

5. Jun 1, 2016

### Hannah7h

Ok cool, thank you

6. Jun 1, 2016

### Staff: Mentor

Ah, ok. So there will be a voltage while it is moving into the coil, but once it stops the flux is no longer changing in time and so the voltage will be 0.

7. Jun 2, 2016

### Hannah7h

Yep this is what i thought, thank you very much

8. Jun 2, 2016

### David Lewis

If the coil is in a closed circuit, then when the magnet stops moving, the current will die off, and the coil will produce voltage via self induction.

9. Jun 2, 2016

### marcusl

No, once the magnet stops and the current has died away, there is no longer any EMF.

10. Jun 3, 2016

### David Lewis

True, but it takes some amount of time (after the magnet stops moving) for current to go to zero. The inductance of the coil prevents current from dropping to zero instantaneously.