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Emf versus Voltage; what's the difference?

Aetherius Lamia

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Posted: Tue Mar 20, 2007 3:08 pm

Emf = Electromotive force?

Voltage = Electric Potential Difference?

What's the difference, exactly? My physics professor hasn't mentioned Emf at all this year, and completely skipped the section in the textbook discussing it. He says instead of the cursive 'E', just read it as delta V, and it's exactly the same thing (just a battery, just a source of voltage), and it seems he's correct.

If this is so, then why does my book even mention Emf, if it's just an outdated synonym for voltage?

Posted: Tue Mar 20, 2007 10:04 pm

As far as I can garner, electromotive force dates back to a time where people were more loose with their definitions because it is not a force in modern terms. It is equivalent to a potential difference (voltage).

The textbook may mention EMF because it is seen as helpful in educating students when they are first introduced to the concepts. It could just be that your professor disagrees and prefers to use the less-misleading terminology.

A Lost Iguana
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shyrazn

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Posted: Mon Apr 30, 2007 4:52 pm

Actually, the emf is the potential difference between the terminals of a source of power, such as a battery. The emf, however, always has some hindrance to completely free flow. The resistance is then designated by the internal resistance. The voltage, on the other hand, is the electric potential difference between any two points, and in these cases, usually from the beginning of a circuit to the end of the circuit (if its closed).

Posted: Sun May 06, 2007 11:13 pm

The way I've always seen it is that EMF is specifically the ideal amount of potential that a voltage cell could produce, ignoring internal resistances, while voltage is the effective potential that the circuit receives from the voltage cell, subject to internal resistances in the voltage cell. The EMF is always larger.

Layra-chan
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