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Course: Physics library>Unit 18

Lesson 2: Discovery of magnetic fields

Tracing a magnetic field

A compass will align with the lines of force around a magnet. How could you do this in 3 dimensions? Created by Brit Cruise.

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• Does the compass still work after being disturbed by that magnet?
EDIT: Thanks for answering (^^)
• That's the point! It changes so that wherever you are, its always moving to point at north. Or south, if there's a magnet nearby.
• Does Radiation effect Magnetism?
• Temperature affects magnetizing. High temperatures (above the Curie Temperature Tc) will demagnetize an object. The object may not melt or transform, into a different material at this temperature, but it will cease demonstrating magnetic properties until cooled. Magnets seem to affect radiation a lot more than radiation seems to affect magnets. We should not forget that from some perspectives, magnetism is radiation.
• what does the question "can you sketch this shape in 3 dimensions" mean?
• I think it is referring to the magnetic field, which is the topic of the next video. The question is meant to be a segue into the next video.
(1 vote)
• Would it be possible to suspend iron particles in some sort of clear gel and somehow insert a magnet in the middle of it and see the magnetic lines form?
• Yes, this can be done. The gel should be fairly thin to allow the suspended particles to move easily. In fact it's a more durable idea, and probably cheaper, to have iron filings in a clear oil (baby oil is often suggested), as the iron filings would rust over time in a watery gel. http://amasci.com/electrom/statbotl.html
You could put the oil with the filings in a beaker and put your magnet in a test tube which you insert in the oil. Or lower it into the beaker from a piece of thread, to get a better three dimensional effect.
• If you held a magnet to a computer, would the data in the computer be erased? If so, how come?
• Spinning hard-drives, as opposed to more modern solid-state drives (SSDs), store data as small areas (like some hundreds of square nanometers) of a magnetic disk having south pole up or north pole up. So south pole up might mean 1, and down would be 0. If you had a really small and sensitive magnet with south pole down, it would be attracted to the small parts of the hard-drive platter that was north pole up, and repelled from the parts that were north pole down.

If you have a really strong magnet (and we are talking really really strong. Normal refrigerator magnets won't damage any computers) you can flip these small areas so they line up like iron filings in a magnetic field, instead of the pattern that represents the files on the computer. This is one of the reasons why you keep computers with spinning, old type hard drives out of strong magnetic fields.
• What could affect magnetism?
• So the magnetic field generated by the magnet interupts the north pole?
• Yes, although the magnetic North Pole is stronger, the smaller magnet is closer, so the compass is pointing to the small magnet. The small magnet interrupts the magnetic North Pole
• Why can't you play with magnets near electronic items?
• Because the hard drive/memory of computers are changed by magnetism.

So if you have a too strong magnets you will erase all the programs/function of the computer.
(1 vote)
• At shouldn't the magnet move if the compass is closer? I am confused.
(1 vote)
• Only the needle of the compass is magnetized, not the whole compass. The magnetic force isn't strong enough to move either the magnet or the compass towards the other. If the entire compass was a magnet, then it would probably be strong enough to cause the items to move. Likewise, If the compass' needle was loose, then it would probably move toward the magnet.