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Started by Dave, May 24, 2018, 03:50:13 AM
Quote from: Dave on June 22, 2018, 12:54:49 PMSuspending one of the bar magnets, from the light fitting and on a length of thread that places it almost exactly at the centre of the room, and placing the bar into the thread loop from either end, the end marked "N" always points North - it is therefore actually the South pole of the magnet.Or the geomagnetic North Pole has flipped to being a South Pole without us noticing and both I and my tablet (and one of two comoasses) have been fooled . . . (I typoed "fooked" there, should have left that uncorrected!)Same result from suspending the horseshoe magnet.So, am I wrong in assuming, as I have done all of my life, that the end of an educational demonstration magnet marked "N" is actually that magnet's North pole - or have the Chinese fouled it up yet again?I will pose this question in an email to "Magnet Expert", the UK sellers of the items. Let us see just how "expert" they are.This does not cover my opposing compasses though.Need more data! More experiments! More compasses! Need an electromagnet that I can see the winding direction on.
QuoteHello Dave,Thank you for contacting us.I can confirm that the North pole magnet will in fact attract to the South section on a compass. These are correctly poled as all products are produced in the same format and are Quality Checked before dispatch.The polarities refer to North and South seeking and as N & S attract, this is why you are seeing this. I hope this information helps Dave.Kind Regards,Nathan Wallace
QuoteThanks for your response, Nathan.Hmm, so now the convention for educational magnets is to mark their "seeking" polarisation rather than their actual? Hmm (again), this is fine for showing that "like poles" (regardless of polarity) repel etc. Removed from all other references you could call the ends "Fred" and "Alice" and demonstrate that there is only room for one Fred (or Alice) in close proximity but that Fred and Alice share a strong mutual attraction.But, were I introducing Hall effect devices that magnet would be "the wrong way round" would it not? The HED only knows it likes a North pole on one side or a South pole on the other, regardess of what we mark the ends of the magnet. Basics, to me, require that the North polar end of a nagnet is marked 'N', it would make no difference to the "like/unlike poles" demo but would now agree with all other, independant, magnetic polarity and strength measuring systems. Sorry, one would still have to explain that the compass needle was "back to front" and why.But then, who am I to question . . . ?Dave
QuoteWhat you have been observing is the behavior of the north and south poles of a magnet. One end of any bar magnet will always want to point north if it is freely suspended. This is called the north-seeking pole of the magnet, or simply the north pole. The opposite end is called the south pole. The needle of a compass is itself a magnet, and thus the north pole of the magnet always points north, except when it is near a strong magnet. In Experiment 1, when you bring the compass near a strong bar magnet, the needle of the compass points in the direction of the south pole of the bar magnet. When you take the compass away from the bar magnet, it again points north. So, we can conclude that the north end of a compass is attracted to the south end of a magnet.This can be a little confusing since it would seem that what we call the North Pole of the Earth is actually its magnetically south pole. Remember that a compass is a magnet and the north pole of a magnet is attracted to the south pole of a magnet.
QuoteAll magnets have two poles, where the lines of magnetic flux enter and emerge. By analogy with the Earth's magnetic field, these are called the magnet's "north" and "south" poles. The convention in early compasses was to call the end of the needle pointing to the Earth's North Magnetic Pole the "north pole" (or "north-seeking pole") and the other end the "south pole" (the names are often abbreviated to "N" and "S"). Because opposite poles attract, this definition means that the Earth's North Magnetic Pole is actually a magnetic south pole and the Earth's South Magnetic Pole is a magnetic north pole.
Quote from: hermes2015 on June 22, 2018, 07:08:34 PMDave, you must be exhausted after all the pole dancing today.
Quote from: Icarus on June 23, 2018, 12:50:45 AMDave there are compasses that are deliberately indexed backward, That is to say that the index mark will indicate south when the direction is actually north. Racing Dinghy sailors often use such evil devices. The racing sailor is more interested in the directions of wind shifts or the tacking angle than he is in knowing which way he is actually going. We are merely racing around a closed course that has buoys with which we are required to pass to our port (left) side. Could it be that your walking stick compass is indexed in that manner?That is not all. In various parts of the world there is magnetic deviation that is the bane of the mariners existence. Most likely the bane of RAF nav people too. You would know about that of course. Then there is the mag interference of ones house. There are metallic objects in the floors and walls that interfere with a perfectly good compass.
Quote from: Icarus on June 24, 2018, 01:25:31 AMAaah Dave you are a slave to convention The Chinese are said to have invented the compass. One can wonder how they had it orientated.
Quote from: Dark Lightning on September 22, 2018, 11:48:57 PMThis all reminds me of teaching magnetostatics in high school many years ago. One of the experiments the kids did was to place a compass inside a tuna can and observe what happens. The iron shields the magnet, and when you move it around, it does not track on the earth's magnetic poles. Two of the boys had a compass that pointed E-W instead of N-S. I had no explanation except that it had possibly been demagnetized and remagnetized across the short way (which makes no sense, BTW- that small a magnetic moment wouldn't have been useful for navigation). The following summer, when going through the cabinets doing general cleanup and looking for whatever apparatus was in them that I could use, I found the cause. There was an immensely strong magnet in the cabinet below where those two were working! That magnet was so strong that if one put a steel ball on it, one could barely pull it off. I worked that into the magnetostatics lecture in the ensuing year. Lots of fun, watching the boys, all macho, trying to get the steel ball off it!