borrowing from tomorrow

[kowalskil@alpha.montclair.edu]

On february 20 Roger A. Pruitt (referring to Ampere before Coulomb) wrote:

> Ludwik, it certainly is worth looking into. However, how do you plan on
> introducing the Ampere without talking about charge per unit time and not
> say anything about Coulombs? I'm interested in seeing how this would be
> approached.

I do not teach in the "ampere before coulomb" way and I have no answers.
But recall the definition of the unit of heat, calorie. It did not say
what the nature of heat is. Perhaps we can begin by observing effects
of "something happening in that wire" and try to quantify it. For example, 
by the rate of heating, by electrochemical effects or by forces between wires. 
How do we guess that something is flowing? In the same way the flow of heat
was initally guessed. Capacitors, and electroplating cells, can be of great 
help. Did somebody recently try to teach "elctricity in motion" before the 
"electricity at rest"? Did it work? What were the difficulties?

But Roger, you did not answer my question. Do you agree that SI is not 
compatible with teching electricity by starting with Coulomb's law. What 
units should we use while introducing the 9*10^9 factor? Ampere? What is it? 
We have no choice but to borrow the unexplained unit from tomorrow. We all 
respect logical consistancy; the idea of understanding is  not meaningful 
without it. I do not want to replace "to understand it" by "to accept it".

The common sequence of teaching electricity forces me to say "accept 4*PI, 
accept epsilon, accept ampere, do not ask me why epsilon is called the 
permittivity of free space". All this is avoidable. The 4*PI, for example, 
would appear naturally in a sequence in which F=B*I*L is one of the initial 
relations. In fact, the 4*PI was put into the Coulomb's law (Haviside ?)
to make sure it does not appear in the above formula. Am I looking for 
trouble with this B*I*L example?  Use another one, if you want.

Yes, many students are trained to accept; they do not feel uncomfortable. 
How do you deal with Ampere and 4*PI*eps in Socratian dialoques, Jack?
Ludwik Kowalski