magnitism

[billwald]

On wire wound electric motors both the rotor and stator draw power. Why isn't power sucked out of the magnet on a permanent magnet motor?

A permanent magnet motor could be built with the magnet replacing the rotor or stator. Why not a motor with a magnet for both? It's a switching problem, yes?

Say a long iron bar, say 1/4th by 1 by 12 inches had one end ground to a point was magnitized and one end wound into a watch spring shape with the point on the inside. would not this pragmatically be a monopole because one pole would be shielded by the metal wound around it?

If a solid iron triangle shape was magnetized along the axis from the base to the apex, would both ends have the same pull, with the pull concentrated on the pointy end and weaker on a per square inch basis on the base end?

 

[Holy Roller]

On wire wound electric motors both the rotor and stator draw power. Why isn't power sucked out of the magnet on a permanent magnet motor?

Because the magnet doesn't provide the power--the stator winding (and the current running thru it) does. Since the magnet doesn't provide the power for anything, there's no power to "suck out of."

A permanent magnet motor could be built with the magnet replacing the rotor or stator. Why not a motor with a magnet for both? It's a switching problem, yes?

Why not a motor with a permanent magnet for both? Because what is there to provide for the electromotive force? In order for the motor to do work (spin around), there has to be something to provide for power. Since magnets and magnetism does not supply power (it merely repels like poles and attracts unlike poles. It also attracts iron), how is there to be any spinning?

Say a long iron bar, say 1/4th by 1 by 12 inches had one end ground to a point was magnitized and one end wound into a watch spring shape with the point on the inside. would not this pragmatically be a monopole because one pole would be shielded by the metal wound around it?

No, because the region nearest the magnet will induce it's own magnetism. Thus, little magnetic properties would be observed along the spiral. Anywhere along the spiral. Including the tip. The longer the iron bar, the more feeble the magnetism. The shorter the iron bar, the stronger the magnetism, but the less induced magnetism, due to less of a spiral. If the iron bar is really short, you will have no spiral (just a bent iron bar), and strong, opposing N and S poles.
Make a bar long enough for a very 'spirally' spiral, and you end up with magnetic lines of force cutting into ajacent parts of the spiral, reducing the magnetic effect at each pole.

If a solid iron triangle shape was magnetized along the axis from the base to the apex, would both ends have the same pull, with the pull concentrated on the pointy end and weaker on a per square inch basis on the base end?

If the iron is axially magnetized after it has been formed into its triangle, placing this magnet under a sheet of paper with iron fillings on top would quickly reveal that the triangle will still have two distinct poles of equal and opposing magnetizing force. Cut off a little tip off any of the three points and repeat the experiment. There will still be a distinct and opposing N and S pole. You can repeat the experiment until you're left with just one atom of iron. The experiment would reveal a little atom with a distinct N and S pole of equal magnetic magnitude.

 

[MorkandMindy]

On wire wound electric motors both the rotor and stator draw power. Why isn't power sucked out of the magnet on a permanent magnet motor?

Either the rotor or the stator can be a permanent magnet, the other part is a coil that works as an electromagnet that keeps changing polarity and keeps the whole thing turning.

With current flowing one way the coil repels the South and goes to the North pole of the permanent magnet. Then the current through the coil reverses and it repels the North and goes on to the next South.

It is changing the polarity that requires electric power so the permanent magnet, which doesn’t change polarity, doesn’t need any power. Many motors do use an electromagnet as a permanent magnet but the power consumption of this item is very small and in an ideal World would be zero.

A permanent magnet motor could be built with the magnet replacing the rotor or stator. Why not a motor with a magnet for both? It's a switching problem, yes?

Yes.

Permanent magnets on both wouldn’t be a motor.

If you had unlike poles facing the two magnets would stick together. If they were like poles facing they would repel, they would just jump apart and given freedom to rotate one would turn around and come back and they would be stuck together. Whichever happened you would be left with a fixed result rather than a moving one.

As you say it is a switching problem, you have to switch magnetic poles around to get things moving again and the power to do that comes from the electricity supply.

Because unlike poles repel you only have to switch one of the poles so really only one of them has to be a coil and the other could be a permanent magnet. The use of wound 'permanent' magnets is often to reduce weight, and these are called 'field coils'. And unlike permanent field magnets, field coils can be adjusted to change the speed range of the motor.

Say a long iron bar, say 1/4th by 1 by 12 inches had one end ground to a point was magnitized and one end wound into a watch spring shape with the point on the inside. would not this pragmatically be a monopole because one pole would be shielded by the metal wound around it?

The magnetic lines still come out somewhere, all would still form complete loops, it's just they would be spread by having more magnetic material around one end and be weaker on a per square inch basis... oh, you are already there:

If a solid iron triangle shape was magnetized along the axis from the base to the apex, would both ends have the same pull, with the pull concentrated on the pointy end and weaker on a per square inch basis on the base end?

Yes, exactly, I like your analysis of the problem. Magnetism is pretty profound stuff.

 

[billwald]

Thanks for the replies.

If two magnetic fields occupy the same space they are added as vector quantities to get the field acting in a specific volume of space? Or do they pass thru each other as waves seem to do? (waves and fields boggle my brain).

 

[[serious]]

Thanks for the replies.

If two magnetic fields occupy the same space they are added as vector quantities to get the field acting in a specific volume of space? Or do they pass thru each other as waves seem to do? (waves and fields boggle my brain).

I believe they are added as vector quantities.

 

[MorkandMindy]

Thanks for the replies.

If two magnetic fields occupy the same space they are added as vector quantities to get the field acting in a specific volume of space? Or do they pass thru each other as waves seem to do? (waves and fields boggle my brain).

Yes right both times.

One field does not keep out the other in any way, they don't affect each other so at a given point the effect is just what one field would give on it's own plus the effect the other would give on it's own.

They are vectors so they add as vectors just like serious said.

_

 

[Holy Roller]

They can't be treated as vectors, since a vector subtraction of like-poles would produce a region where there is no magnetic field. But we all know that fields exists where there are two like-poles, even if the fields are repulsive.

 

[Holy Roller]

Thanks for the replies.

If two magnetic fields occupy the same space they are added as vector quantities to get the field acting in a specific volume of space? Or do they pass thru each other as waves seem to do? (waves and fields boggle my brain).

Waves don't "pass through" each other, as Thomas Young's double-slit experiment aptly proves.

 

[[serious]]

Waves don't "pass through" each other, as Thomas Young's double-slit experiment aptly proves.

now if only we were talking about fields instead of waves...

 

[MorkandMindy]

They can't be treated as vectors, since a vector subtraction of like-poles would produce a region where there is no magnetic field. But we all know that fields exists where there are two like-poles, even if the fields are repulsive.

With two like poles of equal magnitude in the same place you would add the vectors so there would be twice the field strength.

Waves don't "pass through" each other, as Thomas Young's double-slit experiment aptly proves.

The double-slit experiment demonstrates that waves from two sources go through each other and the total field strength at any point is the sum of the contributions from the two waves superimposed at that point and time.

Where the waves match in phase the sum is twice as big and where they oppose the sum is zero.

Or to freeze time and look at it, where the fields are in the same direction the total is twice as big and where they are opposite directions the sum is zero. When a field varies with time it is a wave, owing to the propagation delay.

In both cases I've assumed the sources are equal strengths and we are somewhere roughly equal distances from the sources, if not the 'twice' and 'zero' just become 'bigger' and 'smaller'.

 

[Radagast]

They can't be treated as vectors, since a vector subtraction of like-poles would produce a region where there is no magnetic field. But we all know that fields exists where there are two like-poles, even if the fields are repulsive.

HR, once again you're expressing scientific opinions that are totally off-beam!

I think you're saying (correctly) that vector addition of magnetic fields would give a point between the two magnets with no field. However, you are wrong when you say that doesn't happen:

 

[MorkandMindy]

Just for fun I'll try explaining the pictures in terms of vector addition

diagram 2
Midway between the two N poles there is an equal field vector coming from the left and an equal but opposite one coming in from the right N pole so at that point the two balance and there is zero field.

diagram 1
The N pole produces a magnetic field pointing to the right and the S pole on the other side also produces a mag field pointing to the right, add them up and get a bigger field.

The vector addition seems to work OK

 

[MorkandMindy]

If two magnetic fields occupy the same space they are added as vector quantities to get the field acting in a specific volume of space?

With two like poles of equal magnitude in the same place you would add the vectors so there would be twice the field strength
...

I took the 'same place' perhaps rather more seriously than it was meant, so I wasn't thinking of the space between them but only of the field outside the two magnets.

Here's a simple diagram to explain what I meant by 'twice the field strength', sorry about the lack of lots of nicely angles lines, I'm just not much of a graphics pro yet, and the bar magnets are going through the page for ease of drawing too, maybe someone will improve on it. (I hammered the bar magnets in, hope it doesn't damage your screen.)

 

[Holy Roller]

HR, once again you're expressing scientific opinions that are totally off-beam!

I think you're saying (correctly) that vector addition of magnetic fields would give a point between the two magnets with no field. However, you are wrong when you say that doesn't happen:

LOL
x

!!!

 

[[serious]]

LOL
x

!!!

I'm not so sure what you find amusing. You were quite clearly proven wrong. Don't get me wrong, I find it hilarious, but I'm surprised you are equally amused.

 

[Holy Roller]

I'm not so sure what you find amusing.

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Lulz...