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Re: EMF +- battery speculation



Ludwik wrote describing the Nth reincarnation of Sears and Zemansky:


Two additional arrows appear in this box, they represent
forces acting on charge carriers inside the source. The Fe
arrow is pointing in the same direction as E and it is called
the electrostatic force. The second arrow, Fn, has the same
length as Fe but is pointing in the opposite direction, is is
called the non-electrostatic force. This is Figure 26-10; it
represents the "open circuit" situation.

The next Figure (26-11) shows the same box in the
"complete circuit" situation. This time the Fn arrow
is longer than the Fe arrow. Referring to Fn the authors
write: "this force, operating inside the device, pushes
charges from "-" to "+" in the "uphill" direction against
the electric force Fe. Thus Fn maintains the potential
difference between the terminals. If Fn were not present,
charge would flow between the terminals until the potential
difference was zero. The origin of the additional influence
Fn depends on the kind of source."

How does all this differ from my speculation (see below)?
That speculation was not written after reading the above.
But Sears and Zemansky was the first textbook I used as
a teacher (in 1969) and my ideas were probably strongly
influenced by it.



I think it needs to be remembered that the emf is a black box that may or
may not be a battery, it might be a handcranked generator, or a van-degraaf,
that isn't powered by "electric forces" of the muscles, but could be hooked
up to falling weights . . . I think the need to keep the discussion general
is why they use the emf black box and have a force labeled Fn which may or
may not be electrical in nature (in the sense Ludwik was using).

Joel R