I just got more confused from reading about magnetic field lines' direction over in Wikipedia's dipoles article, including the correcting discussion there.
1) Do magnetic field lines go from the south pole to the north pole in a drawing of a bar magnet but from the north pole to the south pole in a drawing of the earth?
2) Is the north pole in a drawing of a bar magnet positive even with lines north-seeking, while the north pole in a drawing of the earth is negative even with lines south-seeking?
3) Is it only direction (and not electrical charge) which is positive and negative about the magnetic field lines in #1 and #2?
4) When a compass needle points north, is it designed to point in the direction of the earth, although without such rigging it would otherwise point south and be confusing as a navigational tool?
5) Do electrical field lines represent current flow and go from positive charge to negative charge without any such redesigning ever for direction or anything else, as for magnetic field lines?
1) Do magnetic field lines go from the south pole to the north pole in a drawing of a bar magnet but from the north pole to the south pole in a drawing of the earth? The Earth's North Pole is the pole that attracts the north pole of bar magnets in the compass (that is, a compasses north pole points toward's the Earth's). Since opposites attract in magnetism, the Earth's "North Pole" is actually equivalent to a south pole of a magnet.
Now, I'm not quite sure how to interpret your comment about the direction of the field lines. The fields are loops. Inside a bar magnet, they go from south to north. Outside, they go from north to south. I should point out that the fields don't really have a preferential direction - we could just as easily have decided that they point in the opposite direction. As long as we were consistant and always made magnets point that way, we could work equations with that equally well.
I think I've answered #4 as well (let me know if I haven't).
If I understand the question correctly, the answer to #3 is yes.
For #2, I'm not sure I understand what you mean by "lines south-seeking" and "lines north-seeking."
The whole asigning poles as "positive" and "negative" thing, I think, is confusing, which is why I've never seen it in a text book. For one, you're obviously having difficulty separating "positive magnetism" from positive charge. For another, since magnetic fields are loops, they don't really travel just from one pole to the other. In fact, searching for information about positive and negative magnetic poles on Google directs you almost entirely to "magnetotherapy" site that tend to get all the science wrong.
methos: You did a much better job than I ever expected. The link is also helpful. Yet, I have one small question at this time. Would a diagram of the earth (perhaps a circle, with the north pole on the top and the south pole on the bottom) have the field lines moving exactly as in the diagram of the magnet with the field lines above (from the north pole to the south pole on the outside)?
methos: I visited the link, and it claims that the magnetic field lines are the same for the earth as for a magnet: from south to north. Yet, the diagram of the magnet in your post above is from north to south. Okay, which way are the magnetic field lines of the earth and a magnet moving in sync, if they are still moving in sync?
Should we wait for Professor to come to our rescue . . . with more confusion perhaps?
I think that we agree that the magnetic field lines of the earth and a compass are in sync, although the true poles of a compass are relabeled to avoid confusion. Again, are the magnetic field lines of the earth and a magnet in sync, and toward which pole do they conventionally move?
"Should we wait for Professor to come to our rescue . . . with more confusion perhaps?" I resemble that remark. The definitions of magnetic north and south are certainly confusing.
It turns out that you can think of the Earth as having a gigantic bar magnet buried inside. In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole...
...which is what methos said -- near the Earth's north pole there is the equivalent of a magnetic south pole. Hence a magnetic compass's north pole is attracted to the Earth's north pole.
tsaeb, you speak of the field lines "moving" but in reality they are static and not moving. They have directionality, however, so the field lines are "pointing" in specific directions, as generally indicated by little arrows in depictions of the field lines. This may be a trifling quibble, but you see the difference between moving versus pointing, don't you? The lines are oriented but static.
A compass simply measures the orientation of the field at any given location on earth.
Posts: 1911 | Location: U.S. | Registered: 06-03-02
methos and Professor: Let's see how I am doing, whether I am now not confused about the topics at hand.
Ordinarily, a magnet drawn alone and the earth drawn alone, when a magnet and the earth are being compared, have the same poles and magnetic field lines/loops.
I still think that by convention the magnetic field lines outside of the earth point from the south to the north. Anyway, this is the way that I learned it from that "Scientific American" article which Professor sent me to the library to read. So methos's diagram of a magnet has magnetic field lines pointing in the wrong direction in the sense of departing from convention when comparing a magnet with the earth.
In truth, a magnet's south pole must coincide with the earth's north pole. However, a compass outside the earth and tantamount to such a magnet is labeled north at the compass's south pole so that both the compass's and the earth's north pole are communicated in sync to avoid confusion to the person reading the compass.
By convention, magnetic field lines inside the earth should be drawn to point down, while the earth's magnetic field lines outside the earth should be drawn to point up. However, when imagining a magnet inside the earth, the poles and magnetic field lines of the magnet inside the earth and the earth are not in sync and should be imagined to be opposite.
The NASA diagram is truly one of the earth's poles and magnetic field lines, but technically if the magnet is to be imagined inside the earth, the poles of that magnet and its field lines should be imagined as reversed.
This message has been edited. Last edited by: tsaeb,
Originally posted by tsaeb: methos: I visited the link, and it claims that the magnetic field lines are the same for the earth as for a magnet: from south to north.
The only directionality shown in that link is for a picture of a bar magnet. The picture of the earth does not show directionality.
here is a picture that does show the directionality. I did not link to it before because it is not what the Earth's field lines really look like. Notice, in this picture, they have drawn a bar magnet inside the Earth, and notice that it's north pole points towards the Earth's South Pole and its south pole points towards the Earth's North Pole. The picture isn't quite as accurate as the one on the NASA site, because it doesn't show the distortion of the Earth's magnetic field caused by the solar wind. It does, however, show the directionality of the field lines that you are concerned with.
methos: Thanks for returning . . . to this thread. I think that I got the direction of the earth's magnetic field lines "to my satisfaction." However, regarding physics, my mind draws a few blanks. So I'll have to share that Nobel Prize with a physicist, if one can find anything I rant valuable enough on which to expand.
Hmm but magents on their sides can have different pole effects too. One can have 2 sides that attract or repel. It isnt just the 2 poles shown in the picture.
Under the Ocean, There are large deposits of material like giant strips running north to South from new deposits coming up from beneath the Crust, Every so far they are orientated in opposite magnetic directions.
I believe Science takes this as the Earth’s magnetic fields have reversed themselves over the Millions of years back and forth.
But I would question if enough magnetic material was in place next to new molten material coming up. If it would not be like the nearby solid material acting like a giant bar magnet more powerful then the farther away Magnetic field of the earth which is forcing the Molten material’s deposits to turn around, like laying two bar magnets close together, They will force a reversal on each other.
That the Earth’s magnetic field never really reversed itself.
Also Magnetism disappears at 5,000 degrees F. So if the field is present inside the Earth. It must have changed energy form.
I don’t think I have ever seen a magnet in the form of a globe. Might be cute to have one where the Center can be heated above 5,000 degrees and do some checking.
Ken
Posts: 457 | Location: Ilion NY | Registered: 04-18-07
So methos's diagram of a magnet has magnetic field lines pointing in the wrong direction in the sense of departing from convention when comparing a magnet with the earth.
