Question about magnetic fields (electromagnet)

[mburt]

Hi guys,

So far I am aware of these rules regarding magnetic fields/direction of current:

A compass needle point is attracted to a south pole (or inversely repelled by a north pole).

Left hand rule #2: For an electromagnet, point thumb toward north pole, fingers curl in direction of current (up or down the front).

However there is a diagram I've been looking at for some time and I can't figure out how it's possible! I have the answer I just can't work in reverse to try to discover this rule: what effect does moving a permanent AWAY from an electromagnet, with its north pole closest to the electromagnet, regard current direction, and compass deflection (compass placed on the opposite side).

I've attached an image of the diagram with the answer included (multiple choice, it has a check by it).

Thanks,
Mike.

 

[zhermes]

This type of problem is a good deal more complicated than the examples you gave. This involved "Induction", and changing currents, and electric & magnetic fields.

Try reading up on the phenomenon of http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction" which tells you in which direction the currents will be induced.

Once you've done that, ask about anything that doesn't make sense; or if you still have trouble with the problem.

 

[mburt]

Thanks, I'll check that out.

 

[mburt]

Ah, I figured it out! As a magnet moves towards an electromagnet, Lenz' law tells us that the electromagnet's magnetic field will attempt to REPEL the magnet.. (oppose the force)

So if a magnet with a north pole facing the electromagnet was moving AWAY from the electromagnet, the side of the electromagnet facing the moving magnet would attempt to attract it, thus being south. Once that's established the question is easy.

Thanks!

 

[sardar]

Hi Mike,

Thank you for your question about magnetic fields and electromagnets. It sounds like you have a good understanding of the basic rules for magnetic fields and their interaction with compass needles and currents. However, you are struggling to understand a specific diagram and how it relates to these rules.

From the diagram you have provided, it appears that the question is asking about the effect of moving a permanent magnet away from an electromagnet with its north pole facing the electromagnet. In this scenario, the direction of the current in the electromagnet would be the opposite of what you would expect based on the left hand rule #2. This is because the north pole of the permanent magnet is facing the electromagnet, creating a repulsive force. Therefore, the current would need to flow in the opposite direction to produce a magnetic field that would counteract this repulsive force.

As for the compass deflection, it would also be in the opposite direction of what you would expect. Since the north pole of the permanent magnet is facing the electromagnet, it would create a magnetic field that is opposite to the magnetic field of the electromagnet. This would cause the compass needle to deflect in the opposite direction, away from the electromagnet.

I hope this explanation helps you better understand the diagram and the effects of moving a permanent magnet away from an electromagnet. If you have any further questions, please don't hesitate to ask. Keep up the curiosity and great work in your studies of magnetic fields!

Best,