MESSAGES COLLECTED FROM PHYS-L AND TAP-L (physics teacher) LIST SERVERS ***************************************************************************** Date: 14 Aug 96 10:19:50 EDT From: Ann Hanks <73174.2267@CompuServe.COM> To: Multiple recipients Subject: Magnetizer help! Hello Tappers, Remember the discussion about the ETP magnetizer that was wired backward so that it made the North pole into a South pole? I work for PASCO and we sell ETP magnetizers. We checked all of our magnetizers that we have in stock and they are all wired backward. So we complained to ETP and their response was incredible: They said that they knew it was backward. They used to wire it correctly until a customer complained that when they used the magnetizer the resulting magnet was polarized such that the "North-seeking" end of a compass needle (i.e., the North end of the compass needle) pointed toward the South end of the magnet. This is correct but, according to ETP, the general public believes that the "North-seeking" end of the compass should point toward the North end of any magnet! (The people at ETP don't seem to know that the magnetic pole of the Earth in our hemisphere is a South pole.) ETP goes on to say: "...most inexpensive magnets are made with the polarity reversed. So ELECTRO_TECHNIC bowed to the popular perception even though it is counter to the ancient convention. In all the years and thousands of magnetizers sold, the number of complaints about polarity have been very few." Help! Here we are trying to educate the general public while the magnetizer and magnet companies are undermining our efforts. How are we supposed to make things clear to students who have played with reverse -polarity magnets throughout their childhood? Please call or write to ETP, asking them to correct the polarity. Perhaps if they hear from enough of us, they will realize that the only reason that we haven't complained until now is that most of us are capable of slapping a sticker on the front of the magnetizer to show the correct polarity. The address is: Electro-Technic Products, Inc. 4642 N. Ravenswood Chicago, IL 60640-4592 Phone: (312)561-2349 FAX: (312)561-3130 Ann Hanks PASCO Product Development ***************************************************************************** Date: Mon, 4 May 1998 22:36:11 -0400 Sender: owner-phys-l@atlantis.uwf.edu From: jat178@psu.edu (Joe Taylor) To: phys-l@atlantis.uwf.edu Subject: Re: south in the north At 4:13 PM 5/3/98 -0700, William Beaty wrote: >Here is last week's ASK MARILYN column in the sunday paper Parade section. >I've not complained as yet. The email address is marilyn@parade.com > >> WHY DOES THE NORTH END OF A COMPASS NEEDLE ALWAYS POINT NORTH? IF LIKE >> POLES REPEL (AND UNLIKE POLES ATTRACT), SHOULDN'T THE NORTH END POINT >> SOUTH INSTEAD? >> >> The north pole of a compass needle DOES point south. It's the >> "north-SEEKING" pole that points to the Earth's magnetic north. So the >> end of the compass needle marked N (for north) is actually the south >> pole of the compass needle. This is supposed to avoid confusion! William, It is my understanding that the earth's south magnetic pole coincides roughly with the north geographic pole. Therefore, the north pole of a compass needle does point north because it is attracted to the earth's south magnetic pole. This is easily demonstrated by bringing the south pole of a bar magnet near the north pole of a compass needle. The needle will be attracted. Joe Joseph A. Taylor Physics Teacher Middletown Area High School 1155 N. Union St. Middletown, PA 17057 (717) 948-3333 jat178@psu.edu http://www.personal.psu.edu/users/j/a/jat178/ "If I have seen further it is by standing on the shoulders of giants". - Isaac Newton (5 Feb. 1675) GO NITTANY LIONS! , , > ("\''/").___..--'''"-._ > `9_ 9 ) `-. ( ).`-.__.`) > (_Y_.)' ._ ) `._ `. ``-..-' > _..`--'_..-_/ /--'_.' .' > (il).-'' ((i).' ((!.-' > ***************************************************************************** Date: Tue, 05 May 1998 00:48:23 -0400 From: Jerome Epstein To: phys-l@atlantis.uwf.edu Subject: Re: south in the north Joe Taylor wrote: > > It is my understanding that the earth's south magnetic pole coincides > roughly with the north geographic pole. Therefore, the north pole of a > compass needle does point north because it is attracted to the earth's > south magnetic pole. This is easily demonstrated by bringing the south pole > of a bar magnet near the north pole of a compass needle. The needle will > be attracted. > > Joe > Joe Taylor is correct. The magnetic pole near the Earth's North pole is a South Magnetic pole. ***************************************************************************** Date: Tue, 5 May 1998 07:56:45 -0400 From: Chuck Britton To: phys-l@atlantis.uwf.edu Subject: Re: south in the north Please suspend a (correct) bar magnet by a string, somewhere in your classroom. Everyone should be reassured that the N end does indeed point toward the geographic north pole. Paula Abduhl has it right, it's a natural fact that opposites attract. A compass needle is just a small bar magnet. There are far more bar magnets in the world than there are worlds, so the 'convention' has become that the word 'seeking' will no longer be used. Magnetically speaking the bar magnets are labeled correctly and the labels of the earths ends will remain confusing (until the next pole swap occurs, then the Earth's poles will agree, but the compass will then point to where the penguins live.) -. .-. .-. .-. .-. .-. .-. .-. .-. .- \ / \ / \ N / \ C / \ S / \ S / \ M / \ / \ / `-' `-' `-' `-' `-' `-' `-' `-' `-' Chuck Britton Education is what is left when britton@odie.ncssm.edu you have forgotten everything North Carolina School of Science & Math you learned in school. (919) 286-3366 x224 Albert Einstein, 1936 ***************************************************************************** Date: Tue, 05 May 1998 09:36:45 -0400 From: "Hans G. Ammitzboll" To: phys-l@atlantis.uwf.edu Subject: Re: south in the north I guess the point here is that Ms. Marilyn has gotten one wrong YET AGAIN! The end of the compass needle marked N (for north) is in fact, just what it claims to be; the north pole of a small magnet. It points to the Earth's magnetic SOUTH. Which lies in the geographic region of northern Canada. The correct convention for naming poles is to call the end which would point in the geographic north direction, the north pole. This means that the magnetic polarity in that direction must be a south magnetic pole. As an interesting aside, if you ever purchase a "re-magnetizer" for your classroom magnets, you should know that the two wells into which you place the ends of the magnets are marked WRONG. If you hold the north pole of a PROPER magnet near a compass, you will attract the south end of the compass. Since this seems to confuse many people, the manufacturers of these re-magnetizers have switched the labels on their apparatus so that the end of a magnet placed into the well marked N, will come out attracting the North end of a compass needle. Vice-versa for the well marked S of course. Kind of odd reasoning on the part of the manufacturers. I guess they think something like 'since more than half the people get it wrong, we'll switch things around so that we agree with the majority.' Go figure! -- Hans G. Ammitzboll physics@mindless.com Drew University Physics Dept. Madison NJ 07940 "Grow up, not old. Be childlike, not childish." -Me ***************************************************************************** Date: Tue, 05 May 1998 10:08:16 -0400 (EDT) From: LUDWIK KOWALSKI To: phys-L@atlantis.uwf.edu Subject: Re: south in the north Date: Tue, 05 May 1998 09:36:45 -0400 From: "Hans G. Ammitzboll" Subject: Re: south in the north > ... The end of the compass needle marked N (for north) is in fact, just > what it claims to be; the north pole of a small magnet. It points to the > Earth's magnetic SOUTH. Which lies in the geographic region of northern > Canada. The correct convention for naming poles is to call the end which > would point in the geographic north direction, the north pole. A better convention (more general) is to say that the end of a magnet from which the field lines are emerging is N while the end toward which they are converging is S. How can one tell? By watching the compass. The S to N segment of the needle coincides with the direction of B. Ludwik Kowalski ***************************************************************************** Date: Tue, 5 May 1998 10:28:07 -0400 (EDT) From: "Donald E. Simanek" To: phys-l@atlantis.uwf.edu Subject: Re: south in the north On Mon, 4 May 1998, Herbert H. Gottlieb wrote: > >Joe Taylor is correct. The magnetic pole near the Earth's North pole > >is South Magnetic pole. > > Joe IS N OT CORRECT. The magnetic pole near the Earth's North > Pole is a NORTH MAGNETIC POLE. > > Herb Gottlieb from New York City > (Where the Earth's north magnetic pole is close to the > earth's north pole) > We always suspected there was something strange about New York City. I side with Joe on this one. Of course, one could *define* it either way, but the relation of magnetic field to current-carrying wires is defined in one and only one way in all textbooks at all levels, just as is the convention for currents (which many students wish had been done differently). Therefore, we can check our compass' response to current carrying wires, in coils, etc. and determine the direction of the magnetic field "lines" from the magnet, using the standard textbook conventions. Thus we find which end of the compass is the magnetic North end. Then we wee which way that end points. It points to geographic North. This indicates that geographic North of the earth is Magnetic South of the Earth. One of my favorite demos is to check this, starting from scratch. I use a large lecture galvanometer. Of course we don't assume anything about the galvanometer, so we check which deflection is positive and which negative by use of a chemical 1.5v cell. It's quite difficult (impossible?) to reverse the polarity of a chemical cell without drastically tampering with it internally (remanufacturing it), or modifying the laws of electrochemistry. So we can trust that if the cell has a terminal potential of 1.5v, it's polarity is also what it should be. Now we know which deflection corresponds to a particular direction of conventional current. So then I put a loop of wire across the terminals and move that wire through the poles of a strong (magnetron) magnet. The students must predict which direction the galvanometer will deflect if the wire is thrust in a certain way between the poles if pole X is N. Thus we get them to think through the vector relations between v, B, and I, before doing the experiment, and also we find out which pole of our magnet it N. Then I take a small compass and see which end of it is attracted to the N pole of the large magnet. Thus we have found out which pole of the compass is N. Then we move away from all local sources of magnetic field and see which geographic direction the N pole of the magnet points to. If no one has tampered with the compass, one end of the needle has some marking to indicate it is the "north geographic pole seeking" end, and that will be its magnetic North pole. Historically, that's why it was named the "North" end of the compass needle. Only much later did we understand the physics behind it. In all of this we have taken nothing for granted except the equations and current and field conventions of the textbook, and the polarity of our chemical cell. We did not assume we knew the polarity of the large magnet, the compass, or the earth, nor the polarity of the terminals of the galvanometer. Of course the earth has no internal bar magnet, and no "pole" near the arctic and antarctic regions, for the shape of the field is more like that of a dipole. However, using the standard convention, the field lines coming up and out of the earth in the Southern hemisphere have their arrowheads outwardly directed. When I took Freshman physics, Prof. John Eldridge used his own textbook. He told us that in the first printing someone at the printery looked at his diagram of the Earth with a magnet inside and N and S labeled, and saw that S was at the top. Thinking this was wrong, they turned it upside down so N was at the top. Now it happens that N and S are letters which look nearly the same inverted. No one noticed until the copies were printed. Careful examination of the Roman capitals' serifs showed that the N and S were upside-down. Later printings corrected the error. I have copies of both printings. This leads to an interesting joke. Print a label for a package, using Swiss font, saying "up (arrow up) dn (arrow down)" Use lower case for "up" and "dn", and use actual arrows where I've indicated. Put it on the package, and whichever way they sit the package, it will read as if it is correct. The abbreviation "up" inverts to "dn" and vice-versa with non-serif fonts. -- Donald ..................................................................... Dr. Donald E. Simanek Office: 717-893-2079 Professor of Physics FAX: 717-893-2048 Lock Haven University of Pennsylvania, Lock Haven, PA. 17745 dsimanek@eagle.lhup.edu http://www.lhup.edu/~dsimanek ..................................................................... ***************************************************************************** Date: Tue, 05 May 1998 9:05 -0600 From: "Quist, Oren Phys" To: phys-l@atlantis.uwf.edu Subject: RE: south in the north Hans: Thank you for the support. I have thought for a long time that I was the only one claiming the "north" and "south" wells on the re-magnetizer were labeled wrong. It is very easy to check. Just put a current through a wire close to a compass and one can see clearly that the "N" marked compass pole is indeed its north pole. the "north-seeking" verbiage does nothing more than confuse the issue. North is north, and south is sourth, and the magnetic south pole of the earth is in the northern hemisphere. Oren Quist, SDSU ***************************************************************************** Date: Wed, 6 May 1998 11:05:12 -0400 (EDT) From: "Prof. John P. Ertel (wizard)" To: list physics teaching Subject: Re: south in the north On Sun, 3 May 1998, William Beaty wrote: > > Here is last week's ASK MARILYN column in the sunday paper Parade section. > I've not complained as yet. The email address is marilyn@parade.com > > > WHY DOES THE NORTH END OF A COMPASS NEEDLE ALWAYS POINT NORTH? IF LIKE > > POLES REPEL (AND UNLIKE POLES ATTRACT), SHOULDN'T THE NORTH END POINT > > SOUTH INSTEAD? > > > > The north pole of a compass needle DOES point south. It's the > > "north-SEEKING" pole that points to the Earth's magnetic north. So the > > end of the compass needle marked N (for north) is actually the south > > pole of the compass needle. This is supposed to avoid confusion! > Sorry that I have been delayed in answering this one, but we are preparing a final and I was up against the stops. Bill Beaty is a much more forgiving person than I am, I guess. To me, this kind of "Bovine Scatology" (as Stormin' Norman so elegantly put it during Desert Storm) is exactly what makes all our jobs as teachers that much harder. I find it presumptuous, in the extreme, for someone to make such statements without at least checking with someone in physics. A little humility here would help this lady immensely. When it comes to science, I simple can't afford an ego. I'd rather have someone else's correct information than any of my best musings (no matter how carefully I think I have thought them out). Accordingly, just in case it was me that had it all backwards, I checked with a number of colleagues, including a very pleasant gentleman in the "Magnetic Effects" branch of NIST (formerly NBS, and I still can't get used to the name change). The accepted standard is that the "north pole" of a compass needle is defined to be at its North Magnetic Pole and marked as such; i.e., this is "the pole from which lines of magnetic flux emanate" (boy, those folks at NIST sure know how to talk). From this, it must follow that the North Geographic Pole of our earth is a South Magnetic Pole.* Of course, Marilyn may have been trying to point out that the names "north" and "south" are interchangeable as they are purely a convention. However, the convention has already been well adopted! The "north named pole" or a magnetic body (such as a compass needle, a bar magnet, or a current carrying solenoid) is the one which to an external observer appears to be a "source" of lines of magnetic induction; while the "south named pole" is the one which appears to be a "sink". If we look also at the internals of the magnetic body, we see that the field lines are continuous. * Actually, as every Boy Scout knows, "the best average location of the maximum influx of magnetic field" on our earth (read: our North Magnetic Pole) is not exactly at our North Geographic Pole but rather some distance south. This fact together with local variations is what leads to the "declination" and "variation" corrections which may be necessary (depending on the accuracy required) to properly run a navigation or orienteering problem. +=================================+ ERTEL SENDS. /^\-/^\ / \ | * | |#########| =========================== / Prof. John P. Ertel \ / veteran Eagle Scout \ / & Marine Path Finder \ +==================================================+ | jpe@nadn.navy.mil or jpertel@BigFoot.com | | Physics Department, 9C Office : 410-293-6657 | | Michelson Rm-338 DSN : 281-6657 | | 572 Holloway RD FAX : 410-293-3729 | | U. S. Naval Academy Research : 410-293-2759 | | Annapolis, MD 21402-5026 Home : 410-757-6618 | +==================================================+ ***************************************************************************** Date: Tue, 05 May 1998 21:53:31 -0600 From: Jim Green To: phys-l@atlantis.uwf.edu Subject: North/South For the life of me (That is not very good grammar is it?), I can not see why you guys are making this so difficult. The north end of a compass is called the north pole of the compass because it points North!!! Or at least nearly North. It really points toward northern Canada, because of mineral deposits there. Only Canadians are able to explain this weirdness. The French Canadians understand this weirdness best.. The first person to notice this phenomenon was my friend Herbie. He used to live in a region called Magnesia in what is now called Turkey. The region is called Magnesia because there are lots of weird rocks there -- also called magnesia. When the cows eat the grass in this region they produce milk called Milk of Magnesia. Well, one day this friend of mine, Herbie, also weird, suspended one of these weird rocks from a thread (I told you he is weird.) and noticed that it always pointed north. He called the end of the rock which always pointed North "north" -- because it pointed North. He decided to go into business making boxes with suspended magnesia rocks, the north end of which always pointed North (He called the end which pointed North the north end -- because it always pointed North.) He calls these boxes compasses -- and he makes a lot money selling them to mariners and others. If you want to buy one of these boxes, I can arrange it -- for a small fee, of course. Or, for that matter (or any other matter), I do have a few shares of stock in his company left to offer. Now it is true that much later, long after Herbie started his business, it was discovered that like magnetic poles repel, so that the place in Canada where the compass points must be a south magnetic pole. Now back to the French Canadians: Because the south magnetic pole is not centered at the north geographic pole, the axis of the Earth's magnetism does not coincide with the geographic pole axis. And this is why the Earth wobbles and why there are tides. I admit that this does not translate from French very well. Well, OK, his name is not Herbie -- I have changed his name to protect the innocent -- but the rest is absolutely true -- well mostly true. Jim Green (This is only an alias) JMGreen@sisna.com