I mave measured attraction versus distance, my results are a little unexpected and I want to compare mine with someone else's. But I do not know he did similar experiments. If someone could give me a person's name, I will be grateful.
Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
measure magnetic attraction versus distance
- Thread starter jknwhz
- Start date
- Thread starter
- #3
What I expected: what you find in literature: like Newton's gravity law : F :: 1/r^2. Or if you prefer to express that different: In a rotatory symmetric system {\nabla\cdot B == 0} everywhere, the same since there is no source or sink of B outside the magnets.
On log-log paper that gives a line with slope 2:1. For all 6 different sets of magnets the points lie an a perfect straight line, but their slope is alike, but far from 1:2.
What I am after is confirmation that more people have measured that, and if so, how they explain it.
----
By the way: When you let the distance decrease slowly, the magnets (which one?) do the work F * \delta l. Where does that energy come from? The only thing I can think of is internal energy, which means that they grow colder. Has anybody measured that? Does there exist a book on the thermodynamic theory of magnetism?
One more, probably stupid question:
Suppose I have a copper wire from me to the other end of the table, 5 cm above the table. Current from me to the other end, 15 - 20 Amperes.
I move a compass across the table under the wire. Which way can I expect the pointer marked "N" of my compass will point to? Left or Right?
To make sure that my compass 'feels' the circular field I move it to above the wire. As expected the compasneedle turns to its opposite.
It should be a simple question: What do you expect and why:
a. When below the wire, the pointer marked "N" points to my left, when above to my right
or.
b. below to my right right, when above left?
And I will be very grateful to the one who makes me understand the meaning of "Permeability" of "Nothing".
N
On log-log paper that gives a line with slope 2:1. For all 6 different sets of magnets the points lie an a perfect straight line, but their slope is alike, but far from 1:2.
What I am after is confirmation that more people have measured that, and if so, how they explain it.
----
By the way: When you let the distance decrease slowly, the magnets (which one?) do the work F * \delta l. Where does that energy come from? The only thing I can think of is internal energy, which means that they grow colder. Has anybody measured that? Does there exist a book on the thermodynamic theory of magnetism?
One more, probably stupid question:
Suppose I have a copper wire from me to the other end of the table, 5 cm above the table. Current from me to the other end, 15 - 20 Amperes.
I move a compass across the table under the wire. Which way can I expect the pointer marked "N" of my compass will point to? Left or Right?
To make sure that my compass 'feels' the circular field I move it to above the wire. As expected the compasneedle turns to its opposite.
It should be a simple question: What do you expect and why:
a. When below the wire, the pointer marked "N" points to my left, when above to my right
or.
b. below to my right right, when above left?
And I will be very grateful to the one who makes me understand the meaning of "Permeability" of "Nothing".
N
- Thread starter
- #6
Yes, you are right, it is.
But a nobody can build a safe, reliable house, let it be a skyscraper, on a lousy foundation. So before I can do anything I must make sure I understand the foundations in all details.
So please answer the simple questions, you will see they are not as 'silly' as you think they are.
But a nobody can build a safe, reliable house, let it be a skyscraper, on a lousy foundation. So before I can do anything I must make sure I understand the foundations in all details.
So please answer the simple questions, you will see they are not as 'silly' as you think they are.
electricpete
Electrical
On what basis do you expect there will be a force varying as 1/R^2.
It's not a trick question, it's not obvious to me how we would come to that conclusion.
I think you start by drawing an analogy to electrical circuit.
We have two dipoles separated by a distance R >> r where r is the characteristic distance of the dipole.
The far-field behavior for a dipole is 1/R^3 (drops off faster than the point charge 1/R^2 since the effects of the equal/opposite charges of a dipole tend to cancel each other at a distance).
How does the other dipole react to the field from the first? Its reaction can be predicted in terms of a torque based on field strength, dipole strenght, and angle relative to the field. How are we tranlating that torque to a force?
=====================================
(2B)+(2B)' ?
It's not a trick question, it's not obvious to me how we would come to that conclusion.
I think you start by drawing an analogy to electrical circuit.
We have two dipoles separated by a distance R >> r where r is the characteristic distance of the dipole.
The far-field behavior for a dipole is 1/R^3 (drops off faster than the point charge 1/R^2 since the effects of the equal/opposite charges of a dipole tend to cancel each other at a distance).
How does the other dipole react to the field from the first? Its reaction can be predicted in terms of a torque based on field strength, dipole strenght, and angle relative to the field. How are we tranlating that torque to a force?
=====================================
(2B)+(2B)' ?
How many poles are the magnets? For a two-pole/thru-magnetization (point source) the exponent is 3, but generally the exponent is the number of pole-pairs plus 2.
- Status