Re: Textbook goofs

[brian whatcott <inet@INTELLISYS.NET>]

At 15:44 8/5/99 -0700, Leigh wrote:
> If you are using Fishbane, Gasiorowicz and Thornton's "Physics",
> take a look at the box at the top of p. 813. It shows an AC
> cliparound ammeter. In the text it says it works by exploiting
> Ampere's law; the caption under the figure says it works by
> exploiting Faraday's law....

> Leigh

Clip on ammeters have been constructed in two forms, which
may be said to adhere to either Ampere's Law or Faraday's Law.
I expect the diagram to which Leigh refers, shows a transformer
type clip on. They are more numerous. But I do not have his
reference to confirm the configuration.

The clip on ammeters suited to AC operation only are constructed to
employ transformer effect, whereby the insulated wire under test
is coupled as about one half turn of a transformer primary into
the jaws, with an internal secondary also surrounding the steel
 laminations (sometimes ferrite jaws) of the clip.
   This type can be configured as a useful scope current probe.

Springing in a sense from the primogenitor of ammeters, namely,
the compass, a direct sensing magnetic-field clip-on Amperean
ammeter could for illustrative purposes, take the following
impractical form:
in a gap provided opposite the sprung jaws of a clip on ammeter
and oriented east west, arrange a compass. Its deflection
is a function of primary current flow through the jaws. (*)

I prefer to reserve the label "Faraday's Laws' for these:
1) Mass liberated at an electrode is proportional to the
charge transferred by the electrolyte (or current times time)
2) Mass liberated at an electrode is proportional to an element's
atomic weight divided by its valency.

(*) A practical example of an Amperean windingless clip-on is the
"Tong-Test" ammeter, Martindale Electric Co, illustrated in
para 174 p1-61
Crofts' American Electricians' Handbook.
8th Ed. Carr. McGraw-Hill.




brian whatcott <inet@intellisys.net>
Altus OK