What Does Voltage Seconds Represent?

[minifhncc]

Hello,

I've tried looking this up on Google but haven't found anything of relevance.

Basically, I want to know what the unit "Voltage Seconds" (Voltage x Seconds) resembles, if it does.

Thanks

 

[russ_watters]

There is no physical meaning to that that I'm aware of. Voltage is essentially a unit of force.

 

[minifhncc]

Okay, I was asking because I wanted to know what the area underneath of a voltage/time graph means.

http://www.practicalphysics.org/imageLibrary/jpeg350/1560.jpg

Thanks

 

[russ_watters]

Are you sure that's what that graph was about? Maybe it's an RMS depiction? The RMS of a sine wave that peaks at 10 is about 7.

 

[minifhncc]

Okay, I was asking because in class, we did a pract when we were heating water by passing a current through a coil of wires in a bottles. Now, the energy OUT was greater than the energy IN.

My physics teacher stated that this was because the voltmeter measures the maximum voltage, when infact the way that an AC current is converted into a DC current is that the polarity is just reversed 50 times a second, so you get a sine wave that only appears on the top of the X axis. You get what I mean?

This is just out of my own curiosity, not related to any course work.

Thanks

 

[russ_watters]

Okay, I was asking because in class, we did a pract when we were heating water by passing a current through a coil of wires in a bottles. Now, the energy OUT was greater than the energy IN.

That's not possible, so it is good that you are looking for the error. It is either in the measurement or calculation...

My physics teacher stated that this was because the voltmeter measures the maximum voltage...

No, I've never seen one that measures anything other than RMS voltage - though some do that by calculation so if the wave isn't perfect there can be some error.

when infact the way that an AC current is converted into a DC current is that the polarity is just reversed 50 times a second, so you get a sine wave that only appears on the top of the X axis. You get what I mean?

Yeah, but I think a good dc power supply does a little more than rectify the wave, it also chops off the top. In any case, the meter you use should also show the same error in the amperage if it isn't a true rms meter.

 

[Andy Resnick]

Hello,

I've tried looking this up on Google but haven't found anything of relevance.

Basically, I want to know what the unit "Voltage Seconds" (Voltage x Seconds) resembles, if it does.

Thanks

V*s has the same units as W*C (watt-Coulomb) and Joules/Amp. Not sure if there's any fundamental quantity that corresponds to that.

 

[tiny-tim]

voltage second = weber

Hello,

I've tried looking this up on Google but haven't found anything of relevance.

Basically, I want to know what the unit "Voltage Seconds" (Voltage x Seconds) resembles, if it does.

Thanks

Hi minifhncc!

From http://en.wikipedia.org/wiki/Weber_(unit):

Weber (unit of magnetic flux) — The weber is the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.[1]
In SI base units, the dimensions of the weber are kg.m²/s².A. In derived units, they are volt-seconds (V.s).

(and a tesla is a weber (Wb) per metre squared )

 

[cabraham]

Volt-second is equivalent to a weber, as a volt is merely 1 weber/second. When dealing with energy in the magnetic domain, as opposed to electric, voltage is the *rate of change* or "motion" quantity. Current is the "potential", i.e. 1 amp = 1 joule/weber. A weber is the unit of magnetic flux, the magnetic counterpart of electric charge.

Volts per turn is referred to as "electromotive force", aka "emf", and amp-turns is "magnetomotive force", aka "mmf". The "force" nomenclature is colloquial, and not literal. Neith emf nor mmf is actually a "force".

When dealing with magnetic materials, energy density stored in the form of a magnetic field is the product of volt-seconds per meter squared turn and the ampere-turns per meter, which computes to joules per meter cubed. Or volt-seconds per turn times amp-turns is energy in joules.

The B-H curve of a given ferromagnetic material displays the relationship between amp-turns and volt-seconds per turn.

Does this help? BR.

Claude

 

[minifhncc]

Hi,

Thank you for that.

If there was 2A of current passing through the circuit at any given time, what physical quantity would voltage-seconds resemble?

Well, in terms of the power supply, when we connected the DC terminals to an oscilloscope, it showed that there wasn't a constant current, the polarities being reversed was shown. Yes I think they're pretty cheap power packs.

Thanks.