Re: [Phys-l] Capacitor problem reprise

[John Denker <jsd@av8n.com>]

On 03/28/2008 11:05 AM, mrmeyer@mtu.edu wrote:

> In physics classes we often use schematic symbols to represent
> real objects rather than terms of an equation.  

Sometimes we do it one way, sometimes the other.

>  It is an interesting
> difference of perspective but is not the essential physics.
> I also wish to avoid issues of small effects versus big as
> this distracts from the understanding.  

Then I will have nothing more to say about this circuit.

I know a thing or two about electrical engineering, and about 
physics, and I know that they both require making approximations.  
They require figuring out, in each particular case, what is a
good approximation and what is a bad approximation.

> Therefore I present
> a closely related problem without symbols

Suit yourself.  A picture is often worth a thousand words, but 
if you want to paint a word-picture instead, you're welcome to
try.

OTOH I tell students again and again and again that they should
start by drawing the diagram.  It amazes me that students often
try to get away without the diagram in situations where highly
skilled engineers would draw the diagram.

>  where numerical
> values are not an issue.

Numerical values are always an issue ... especially when recent
history suggests there are misunderstandings about what is a 
macroscopic zeroth-order normal effect and what is a microscopic 
Nth-order junk effect.

There is no problem on earth that can be solved if normal contributions
are deemed small and stray contributions are deemed large.  There's
nothing new or interesting about that.