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Expert: Daniel Mazur - 12/6/2006


Question
But Potential difference is produced due to emf?Please explain more.I will be thankful to you.
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The text above is a follow-up to ...

-----Question-----
What is difference between EMF and POTENTIAL DIFFERENCE?
-----Answer-----
The EMF is a "type" of potential difference. Potential difference is the basic expression, whether we speak of a battery voltage or a voltage drop across a resistor. EMF is a term only used with sources of potential difference: batteries, alternators, dynamoes, generators in general. It is never used with passive elements.
Take care!
Daniel

Answer
Hi,

as you posted a followup, may I ask you to tell me, what led you to lowering my rating? I really would like a feedback, especially about knowledge and politeness. I hope you accept my request, I can hardly ask feedback from those who gave me 10s.

There is a confusion in terminology: The expression "EMF" suggests that EMF is of the units of FORCE. This is NOT true! EMF is called "force" for historical reason, while it really IS a potential difference. An undergraduate textbook (Halliday-Resnick-Walker) says:
"To produce a steady flow of charge, you need a 'charge pump', a device that ... maintains a POTENTIAL DIFFERENCE between a pair of terminals. We call such device and EMF device."

For use in equations, definition of EMF is

EMF := d(Work)/d(charge) ,

which you can easily see are units of POTENTIAL DIFFERENCE, that is, in VOLTS!!! Simply, EMF is (yes, IS, not "produces") a potential difference between terminals of an electrical power supply. For real life you can forget all about confusing EMF, just replace it by "battery potential difference" (or "power supply voltage") whenever you see it and move on.

Cheers!
Daniel

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Questions anyone (teenager, undergrad, graduate, professional) may ask on physics, mathematics or inorganic chemistry. Questions may concern subjects themselves or a possible future career in them, if you need advice on a school or hobby project, or you just came across a question that is beyond your current curriculum. I answer bare textbook problems sometimes, but I reserve the the right to redirect you to Physics-Physics section. The kind of questions I like to answer: I just started having science classes at school and they seem difficult, but I enjoy them. Where do I find more information on this, which is not in textbooks but still comprehensible to me? Just leaving high school, and I feel science is really the thing for me. Can you recommend a school and an undergrad program suitable to my inclinations? I am in my second undergraduate year in Physics. We learned the basics of universe expanding this year, the Hubble constant and all that, but invited speakers that gave talks on astrophysics in our department seemed not to agree with this model at all. Is it of any use at all? I am building a [materials research] experimental device for my masters/doctorate thesis and I have the following problem:... I have tried ..., but it still doesn't work. Where might the problem be?

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