Attraction between a charge and a magnet

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Discussion Overview

The discussion revolves around the interaction between a charged metal sphere and a compass, exploring the nature of the forces involved, including electric and magnetic interactions. Participants examine the implications of the materials involved and the behavior of the compass needle in response to the charged object.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes an experiment where a positively charged metal sphere attracted both ends of a compass, suggesting an electric interaction due to the attraction of electrons in the compass to the positive charge.
  • Another participant questions the material of the metal sphere, asking if it was made of steel or iron, which could influence the interaction.
  • A suggestion is made to repeat the experiment with an unmagnetized needle to determine if the compass needle carried a net charge, emphasizing the importance of stating assumptions in the report.
  • It is proposed that the compass needle's behavior indicates that the magnetic field around the charged object is not dependent on which pole of the compass is closer.
  • Participants discuss the effect of a neutral conductor being brought close to a charged object, referencing the behavior observed in an electroscope.
  • Questions are raised about whether a magnetic field affects a charged object that is not magnetic, and vice versa, with some participants noting that a changing magnetic field can influence charges in a conductor.
  • There is a suggestion that if the charged sphere is made of iron or steel, the compass needle would be attracted even without the charge, indicating a potential induction effect.
  • Participants note that the compass needle's deflection could still occur even if the compass is held still, due to the initial motion and the resulting magnetic field interactions.
  • One participant expresses appreciation for the complexity of the discussion, acknowledging that it raises more questions than it answers.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the nature of the interactions between the charged sphere and the compass, with no consensus reached on the exact mechanisms at play or the implications of the materials involved. Multiple competing views remain regarding the roles of electric and magnetic forces.

Contextual Notes

Limitations include assumptions about the neutrality of the compass needle, the specific materials of the charged sphere, and the effects of motion versus static positioning of the compass in relation to the charged object.

DRC12
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In physics lab we positively charged a metal sphere then placed a compass near it and both ends of the compass were attracted to the sphere. I know magnetic fields are created by electrons, so I made the assumption the compass is attracted to the positive charge because the electrons in the compass are attracted to the positive charge thus the interaction is purely electric. I'm not sure if magnets are negatively charged thou. Is this the basic idea? Or does it have to do with the interactions between magnets and electric charges?
 
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Was the metal sphere made of steel or iron?
 
You should have repeated the experiment with an unmagentized needle ;)
How would you determine if the compass needle carried a net charge?

Anyway - assuming you cannot do more experiments before you need to hand in your report for this one, you can assume the compass needle had a neutral charge (but you should state that assumption in the report). It is also a metal - a conductor.

Before you start thinking in terms of charges on the compass needle - what determined which pole was attracted to the charge? Something about the way you positioned the compass? Since neither pole was favored - what does that tell you about the magnetic field about the charged object?

Now back to considering charges...
What happens when a neutral conductor is brought close to a charged object?
(You've probably seen the effect in an electroscope - but what causes it?)
 
First, so no-one gets angry at more for posting homework in the non-homework section, this isn't for a report I'm just trying to figure out what was going on. The magnetic field on the charged object is unaffected by which end of the compass is closest to it. Because the compass is a conductor, when it's brought near the charge the electrons gather towards the positive charge creating a force on the needle to go towards the charge. So this means it doesn't matter whether the charge was positive or negative, because if it was negative the electrons in the compass would have moved as far from the charge as possible i.e 180 degrees from the charge.
 
Another small question, does a magnetic field have an effect on a charged object that is not magnetic? and vice-versa
 
DRC12 said:
Another small question, does a magnetic field have an effect on a charged object that is not magnetic? and vice-versa
Perceptive question - a changing magnetic field will affect the charges in a conductor. When you bring the compass needle close, you are changing the magnetic field at the charged sphere.

This is why I asked you about what determined which pole was attracted and why (probably) @technicion asked if the metal sphere was iron or steel.
 
Yes...it would be interesting to know what the charged sphere was made of.
If it was iron or steel then the compass needle would be attracted even if the sphere was not charged
 
Simon Bridge said:
Perceptive question - a changing magnetic field will affect the charges in a conductor. When you bring the compass needle close, you are changing the magnetic field at the charged sphere.
But if the compass is still then the magnetic field isn't changing is it? The compass was brought towards the charged object and then held there.

technician said:
If it was iron or steel then the compass needle would be attracted even if the sphere was not charged
Because the magnet would induce a magnetic field in these metals? and all the lab manual says is that the sphere was conducting
 
DRC12 said:
But if the compass is still then the magnetic field isn't changing is it? The compass was brought towards the charged object and then held there.
That's right - but the effect of the motion can still result in a deflection of the needle.
If the compass was oriented so the north pole was initially closer to the charged sphere but the south pole ended up attracted to the sphere, then there could have been an induction effect.
Because the magnet would induce a magnetic field in these metals? and all the lab manual says is that the sphere was conducting
... so if this was a long-answer in an exam, you'd do well to mention the possibility that the conducting sphere has some iron in it.

You should be able to see that quite a lot of things could have been happening.
 
Last edited:
  • #10
Well thanks a lot there's clear's things up
 
  • #11
That's the fun part of asking scientists about something - you end up with more answer than you bargained for :)
 

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