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Re: B and electric charge

Dear Professor Kowalski-

On Sun, 3 Mar 2002, Ludwik Kowalski wrote:

Hi .... (I used to address you as Jack but you are addressing
me by the title. Should I start doing the same? I hope not.)

Please address me as you would any other student.


I said "measure the speed and calculate" the elctric current of
a known charge. I did not say "measure the magnetic effect"
of such current. But I know that others have done this about
a century ago.

I guess I misunderstood. I thought we were doing something
equivalent to the way we discovered coulomb's law. What do I learn from
calculating the current? And what does this have to do with magnetism?

Jack


Let us exagerate and assume that B=1T, that the net Q on
your long rod is 10 nC/m and that you can push the rod with
the speed of 2 m/s. How large is the convection current?
Assuming the stick is pushed along its axis the current is
20 nA. The expected force on the magnet is very small. How
large is the current of the classroom Van de Graaff belt ?
Ludwik Kowalski

Jack Uretsky wrote:

Dear Professor Kowalski-
Thank you for telling me about convection currents. Just
to see how your experiment worked, I rubbed a long plastic tube with
a handkerchief until it was electrified enough to make some scotch tape
move. Then I waved the tube real hard under a refrigerator magnet that
was suspended by a thread. The magnet didn't move until I hit it by
accident. I don't think that's what you meant.
My friend Linda said that it's the v/c that counts. But she's
just a girl, so what does she know? I mean about plastice tubes and
stuff like that. She's really pretty smart about some things.
Your student,
Jack

On Sat, 5 Jan 2002, Ludwik Kowalski wrote:

In the context of this discussion I would
focus on a "convection current", for example,
a long dielectric stick whose charge per
unit length is known. Measure its speed and
calculate the current in C/s. Convection
currents have been studied about a century
ago and they were shown to produce the
conventional (expected magnetic effects.
Ludwik Kowalski

----- Original Message -----
From: Jack Uretsky <jlu@HEP.ANL.GOV>
Date: Saturday, January 5, 2002 11:03 am
Subject: Re: B and electric charge

Here's one waiting for your return:
How about going in baby steps, though, like you're the
teacher and
I am trying to understand what you are doing (not much of a stretch).
We've agreed on definition of charge, as described previously.
The arbitrary constant is 25 N-m^{2}/C^{2}; an equal charge pair
givinga force of 1 N at a separation of 1 m is 1/5 C. Now I hear
you talking
about currents. How do I measure a current (I understand that it is
"flowing charge" and 1 A = 1 C/s)?
How do you answer your student?
Regards,
Jack


On Fri, 4 Jan 2002, Ludwik Kowalski wrote:

Ludwik Kowalski wrote:

What I would like to discuss is the definition of B.
Why do we define it in terms of the EFFECT of the
magnetic field and not in terms of what CAUSES it?
Instead of introducing B via the Lorentz law (directly
or indirectly) we can introduce it via the Bio Savart
law. Which way is pedagogically more desirable and
why? I have no opinion so far.


--
"But as much as I love and respect you, I will beat you and I will kill
you, because that is what I must do. Tonight it is only you and me, fish.
It is your strength against my intelligence. It is a veritable potpourri
of metaphor, every nuance of which is fraught with meaning."
Greg Nagan from "The Old Man and the Sea" in
<The 5-MINUTE ILIAD and Other Classics>


--
"But as much as I love and respect you, I will beat you and I will kill
you, because that is what I must do. Tonight it is only you and me, fish.
It is your strength against my intelligence. It is a veritable potpourri
of metaphor, every nuance of which is fraught with meaning."
Greg Nagan from "The Old Man and the Sea" in
<The 5-MINUTE ILIAD and Other Classics>