Physics - Magnetic Compass?
How can the way the needle points be completely reversed? Am I understanding the question wrong?
Some compasses have mechanisms that can prevent their needles from turning. If you lock a compass's needle in place and pass its north pole near the north pole of a very strong permanent magnet, you will spoil the compass. When you release the needle, it will point toward the earth's south geographical pole. What will have happened to the needle?
Thank you for any clarification.
Update:Also, are compasses affected by nearby electrical currents because electrical currents can create magnetic fields around them?
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Opposite poles of magnets attract each other. The needle aligns to the local magnetic field::
The Earth's north magnetic pole is described so because it is a 'north attracting' pole which means it attracts the 'north' pole of a magnet so it is in reality a magnetic south pole.
Likewise the south magnetic pole of the Earth is a 'south attracting' magnetic pole so it's really the north pole of a magnet.
http://www.tpub.com/neets/book1/chapter1/1g.htm . . ..
The compass needle is a bar magnet having north and south poles, of which the north pole of the magnet points to the north magnetic pole of the Earth so that end of the compass needle is labeled 'north'.
The convention used in labeling north and south poles of magnets is that the 'north' pole of the magnet points to the 'north' pole of the Earth so it can confusing at times.
It doesn't matter which way round the labels are. They work the same both ways. The poles are equivalent to each other so it's just the labeling that gets odd.
Electricity is the 'wrong' way round too....the charge is carried by electrons but positive and negative were already labeled one way round before that was known and it was the 'wrong' way for some purposes so now electrons are called negative and the flow of electrons which makes an electric current is the opposite way round than the positive to negative idea that got labeled that way round long ago....it really goes from negative to positive.
A better way to think is that it goes from the high voltage end to the low voltage end...and so it can affect magnet orientation
Scroll down to :::Conventional electric current
http://hyperphysics.phy-astr.gsu.edu/hbase/electri... : :::
If the Earth's magnetic poles flipped over, which they have in the past, you wouldn't know about it unless you used a compass and noticed the wrong end pointed north.
http://uk.answers.yahoo.com/question/index;_ylt=Au... . . . .. .
If you remagnetise the magnet by using a stronger magnet or with an electromagnetic coil so the magnetic poles are reversed, then if the red-painted end pointed north before it will now point south.
All you have to do is to rub the paint off the red end and paint the other end red or simply remember that the red end is now the south end and the other end is the north end.
When you make a compass needle you don't have to know which end is which....you can test it with a known magnet or simply mount it in the compass and see which end points north and then label it N or paint it red or white or however you want to distinguish one end from the other.
You can find north easily enough by knowing which sides of the sky the Sun rises and sets or where it is at midday or at night by finding the Pole Star or a known southern sky star like Sirius or Formalhaut or a hundred others.
You can de-magnetise the needle easily by putting it in an AC electric field. Tape recorders and tape video recorders have magnetic recording heads which for high quality recordings have to be demagnetised at regular intervals.
All you do is to put a high frequency AC field close to it, which is got from a small contraption you can buy or make.
One guy here is worried about the AC field damaging the transistors but only a tiny bit of power is needed to demagnetise recording heads found in home-use recorders.
http://www.vintage-radio.net/forum/showthread.php?... . . .
When using a compass make sure there are no electrical fields that are strong enough to deflect the needle, or magnetic materials like steel and iron close by. Walk away from cars and especially from hundred-ton trains.
On a ship the compass is surrounded by metal and noting the compass deviation it causes is quite a long task done by people who specialise in it.
The ship is turned to all points of the compass and the compass deviation is marked on a card placed near the compass or on a ring surrounding it.
Compass deviation is not the same as magnetic variation.
Every ship must have it's compass deviation checked for all points of the compass before it can safely go to sea if it has a magnetic compass:
There are books about it:::just adjusting compasses
http://www.archive.org/stream/handbookofmagnet00sp... . . . .
More about compasses
http://uk.answers.yahoo.com/question/index?qid=200... : :: :
Compass needles are made by taking a piece of iron and magnetizing it with a strong magnet/electromagnet. So it is quite easy to re magnetize it with the poles reversed by placing a compass needle next to a permanent magnet/electromagnet.
The needle would then point South.
Yes, nearby electrical currents could affect a compass. The current would need to be strong and probably in the form of a coil. If the current is AC, then it would have the effect of de-magnetizing the needle.
How can the way the needle points be completely reversed? Am I understanding the question wrong? Answer.... Switch the pointer polarity to south, then it would point south. Yes local magnetic devices can interfere with a compass.
To help you i point on sun and clock.(and to save)