I think Wbahn had it right--"EMF" (electro-motive force) is supplied directly by the source, whereas "voltage" is the potential difference between two points (this may be measured directly across the source and, assuming no resistance in the connections, will have the same value as the EMF).

 

Lol, you took my quote where I say "if the generator is not hooked up to anything" and then you hooked it up to a voltmeter.

That seems a little bit not fair.

True. Your hypothesis is correct, but, proving it would be difficult, as proof would require a measurement of some sort.

 

I think Wbahn had it right--"EMF" (electro-motive force) is supplied directly by the source, whereas "voltage" is the potential difference between two points (this may be measured directly across the source and, assuming no resistance in the connections, will have the same value as the EMF).

The part in bold is problematic. In the case of induced EMF, the potential is non-conservative. Hence, the potential reading would depend on the loop created by the meter and leads.

 

what difference does it make what you call voltage with current flowing or not? emf is voltage, regardless of the source and regardless of amount of current flowing. arguing semantics is not anything to do with electricity, electronics, or circuits, and will only take up space on a hard drive somewhere. if you measure the voltage between two points, you are measureing the emf. whether the two points are a battery, generator, powe supply, or across a resistor in a circuit, emf is still another name for voltage.

 

I think Wbahn had it right--"EMF" (electro-motive force) is supplied directly by the source, whereas "voltage" is the potential difference between two points (this may be measured directly across the source and, assuming no resistance in the connections, will have the same value as the EMF).

I don't think they are used interchangeably very often by someone like him who knows when to use each term and why when you see the term EMF instead of voltage it's time to be careful with even simple things like the reading on a voltmeter to find the operating conditions of a circuit.

 

learn the laws of ohm, kirchov, and such to use your measureing equipment properly to avoid ciruit loading and such. then semantics wont matter. potential voltage cannot be mesasured, because the act of measuring loads it down with current. if you actually understand measurements, you can get an idea of what the measureing equipment is actually reading. thats why most of the modern dvm's are 1 meg input, instead of the 1k ohm per volt, 10 k ohm per volt, 11 meg ohm per volt vtvm and such that required you to know what the load was on the circuit under test.

 

both emf and voltage are same? if its not so explain the concept clearly..

Your confusion is down to "conventionalized laziness" (not your fault!)


EMF is the quantity in question (To Wit: ElectroMotive Force) the Volt is a unit thereof! -- Simple as that!!!

Personally, I dislike (and eschew) use of the word "Voltage" (all the same 'Amperage', 'tonnage', 'acreage', 'yardage' etc...)

We don't say 'litreage' for volume, nor 'Newtonage' for force, nor 'metre per secondage' for velocity nor dollarage for price/expense/wealth, nor 'yearage' for time etc...

IMNSHO Convention is neither a substitute for -- nor an excuse to abandon -- literacy!

Best regards
HP

PS -- I apologize should this post be redundant -- I hadn't time to read the entire thread...

 

... arguing semantics is not anything to do with electricity, ...

It's not purely a semantic issue because of the non-conservative nature of EMF induced via time changing flux (Faraday's Law). You need to be careful in defining how you make a measurement with a meter in this case.

if you measure the voltage between two points, you are measuring the emf. whether the two points are a battery, generator, power supply, or across a resistor in a circuit, emf is still another name for voltage.

This is not always true for the case of a generator.

 

It's not purely a semantic issue because of the non-conservative nature of EMF induced via time changing flux (Faraday's Law). You need to be careful in defining how you make a measurement with a meter in this case.



This is not always true for the case of a generator.

With gunine respect: yes it is! 'Voltage' is a back-formed vulgarity that, owing to long use, we're stuck with! -- Why create a 30+ post thread in response to a simple request for clarification???

 

arguing semantics is not anything to do with electricity, electronics, or circuits, and will only take up space on a hard drive somewhere.

Buy that man a Miller! -- Which is to say I AGREE!!!

 

This sounds a lot like the difference between potential energy and kinetic energy. That 1000 pound anvil above your head suspended by a thread has zero kinetic energy...UNTIL
TOUCH the output of that generator or put a volt meter on it and you discover the voltage, until it actually moves a charge it is just potential.

 

Personally, I view voltage as a general term that can apply to potential voltage, or emf voltage. I think of EMF as anything that is not potential. I view potential energy as the conservative force potential energy (per unit charge).

You are confusing the concepts of potential and kinetic energy. If I have a reservoir of water at the top of hill, that water has gravitational potential energy relative to the water turbine at the bottom of the hill whether the valve connecting them is open or not. It is called "potential" energy precisely because it has the "potential" to transform energy from one kind to another -- whether that is actually happening at the moment is irrelevant.

 

Lol, you took my quote where I say "if the generator is not hooked up to anything" and then you hooked it up to a voltmeter.

That seems a little bit not fair.

It doesn't have to be hooked up to anything or, even if it is, there doesn't have to be any current flowing. The E-field could be mapped between the terminals or a nulled galvanometer used to measure the voltage without drawing any current at all. The voltage could also be determined via calculation to at least get a close estimate.

 

This sounds a lot like the difference between potential energy and kinetic energy. That 1000 pound anvil above your head suspended by a thread has zero kinetic energy...UNTIL
TOUCH the output of that generator or put a volt meter on it and you discover the voltage, until it actually moves a charge it is just potential.

Inasmuch as the Volt, by definition, is a unit of EMF -- 'Voltage' and EMF must, perforce, be synonymous in all cases -- whether potential, dynamic or what have you...

 

but the actual energy changes as soon as you open the valve and water starts flowing. that is when the change from potential to actual energy is made. just like a battery with a potential of 1.4 volts, according to chemistry of the metreials the battery is made up of, but when you actually measure it, it might be a little less because of the current drawn by your voltmeter.

 

My view is:

From Master Glossary, Module 20 of the Neets books:
ELECTROMOTIVE FORCE (emf)— - The force (voltage) that produces an electric current in a circuit

VOLTAGE— - (1) The term used to signify electrical pressure. Voltage is a force that causes current to flow through an electrical conductor.
- (2) The voltage of a circuit is the greatest effective difference of potential between any two conductors of the circuit

This would seem to underscore my assertion that there is no significant distinction between these two terms.

Consider the following exam questions drawn directly from those definitions:

1) The force that produces an electric current in a circuit is called ________________.

2) A force that causes current to flow through an electrical conductor is called _____________.

Is the answer to the first clearly "emf" and the answer to the second clearly "voltage" and reversing them would clearly be wrong?

 

Let's take the case of an EMF generated by a generator. If the generator is not hooked up to anything, then there are very few charges that are actually at a potential voltage corresponding to the EMF voltage. However, close the circuit, and the charges in the current are given the potential energy to do work (create kinetic energy in the charge for example, or heat up a resistor, as the charge loses energy)

How many charges are at that potential is immaterial -- ANY charge that is at the positive terminal has the POTENTIAL energy to do THAT much work in going from that terminal to the negative terminal (along the same path along which the potential was determined in the case of a non-conservative field). Remember that EMF/voltage is not a measure of potential energy, but rather a measure of potential energy PER UNIT CHARGE, so whether we are talking about a microcoulomb or a megacoulomb is irrelevant.

 

This would seem to underscore my assertion that there is no significant distinction between these two terms.

Consider the following exam questions drawn directly from those definitions:

1) The force that produces an electric current in a circuit is called ________________.

2) A force that causes current to flow through an electrical conductor is called _____________.

Is the answer to the first clearly "emf" and the answer to the second clearly "voltage" and reversing them would clearly be wrong?

0.5 credit for either way as that would equal to 1.0 in some jurisdictions.

 

0.5 credit for either way as that would equal to 1.0 in some jurisdictions.

Please forgive the use of an internet meme....

 

but the actual energy changes as soon as you open the valve and water starts flowing. that is when the change from potential to actual energy is made. just like a battery with a potential of 1.4 volts, according to chemistry of the metreials the battery is made up of, but when you actually measure it, it might be a little less because of the current drawn by your voltmeter.

What is "actual energy"? Do you mean energy that is actually performing work? Well, work is just energy being transformed into some other form -- kinetic energy of the flowing water, kinetic energy of the moving turbine blades, magnetic potential energy in the generator windings, electric potential energy in the output voltage of the generator, kinetic energy of the moving electrons in the wires, thermal energy in the various resistances involved. At any given moment in time there are lots of different forms of energy at play and the sum of all of them remains exactly the same.

The notion of "actual energy", say the kinetic energy of a moving object, is just as nebulous as the notion of "potential energy". What is the "actual energy" of a bullet that hasn't been fired but is in a box of ammo in the cargo hold of an aircraft traveling 500 mph? In either case no work is being performed by the bullet and so you need an arbitrary reference to talk about it's energy at all, be it kinetic or potential. But when you are talking about energy conversion you don't (I think that is a true statement, but there may well be situations that I'm overlooking in which you do).