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Definition of potential difference

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sram

Member
As most of you know, potential difference is the work needed to move one electrical charge from one point to another.

Is there anything wrong with using the exact same definition, but use the word energy instead of work? To my knowledge they are used interchangeably, and both use the same unit which joule.

It is just that work is the energy expended to perform something.

Reason I'm asking(I'm debating with someone)

Thanks.
 

ericgibbs

Well-Known Member
Most Helpful Member
As most of you know, potential difference is the work needed to move one electrical charge from one point to another.
Thanks.

Where have you read potential difference defined as that.:confused:

**broken link removed**
 
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ke5frf

New Member
Potential difference is not work, and is not exclusive to electronics or electricity. It a elementary physics term used to describe the degree of "opportunity" for stored energy to be "released".

Other forms of stored energy can be measured in terms of potential, like heat, air, and fluid pressure. Even an apple dangling from a tree is described as having potential. Where the word difference comes in is when the potential of the stored energy is measured vs. another state of potential (or lack thereof). We also use the greek word DELTA in those terms. As in temperature PT being DeltaT.

So, as in temperature, when a hot baked good is brought out of the oven at 100 deg C, into an ambient environment of perhaps 22 deg C, we say the DeltaT (or PT) is 78 deg C. This is because we know that an exchange of that energy will occur, with heat being the ENERGY, and the nature of heat being to flow from warm to cool. So the faster moving molecules that are heated will collide with cooler, slower molecules and eventually the energy will be dissapated to near ambient.

If a balloon is filled to a pressure of 20 psia (lbs/sq inch atmospheric) vs 14 lbs of atmospheric pressure in the environment, there is 6 lbs of potential or DeltaP of 6 psig (lbs/sq inch gauge), with atmospheric referred to as 0 psig.

Energy is not potential but can be described in terms of it when it is stored. But energy is not stored when it is doing work, so it is obvious that it can't be called potential, The two are related but not the same.
 
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As most of you know, potential difference is the work needed to move one electrical charge from one point to another.

Is there anything wrong with using the exact same definition, but use the word energy instead of work? To my knowledge they are used interchangeably, and both use the same unit which joule.

It is just that work is the energy expended to perform something.

Reason I'm asking(I'm debating with someone)

Thanks.


Potential from a to b, electric potential that is, is the work per unit charge, associated with transporting said charge from a to b. A volt is a joule per coulomb. Potential is not the same as energy/work, but related to it.
 

sram

Member
Where have you read potential difference defined as that.:confused:

**broken link removed**

Potential difference is not work, and is not exclusive to electronics or electricity. It a elementary physics term used to describe the degree of "opportunity" for stored energy to be "released".

Other forms of stored energy can be measured in terms of potential, like heat, air, and fluid pressure. Even an apple dangling from a tree is described as having potential. Where the word difference comes in is when the potential of the stored energy is measured vs. another state of potential (or lack thereof). We also use the greek word DELTA in those terms. As in temperature PT being DeltaT.

So, as in temperature, when a hot baked good is brought out of the oven at 100 deg C, into an ambient environment of perhaps 22 deg C, we say the DeltaT (or PT) is 78 deg C. This is because we know that an exchange of that energy will occur, with heat being the ENERGY, and the nature of heat being to flow from warm to cool. So the faster moving molecules that are heated will collide with cooler, slower molecules and eventually the energy will be dissapated to near ambient.

If a balloon is filled to a pressure of 20 psia (lbs/sq inch atmospheric) vs 14 lbs of atmospheric pressure in the environment, there is 6 lbs of potential or DeltaP of 6 psig (lbs/sq inch gauge), with atmospheric referred to as 0 psig.

Energy is not potential but can be described in terms of it when it is stored. But energy is not stored when it is doing work, so it is obvious that it can't be called potential, The two are related but not the same.



Shooooot! I actually meant to say the electric potential difference, not just the potential difference. Sorry I thought it was clear since It was posted here.

**broken link removed**

Back to my original question, do you see now what I meant by it?


Thanks.
 

crutschow

Well-Known Member
Most Helpful Member
Shooooot! I actually meant to say the electric potential difference, not just the potential difference. Sorry I thought it was clear since It was posted here.

**broken link removed**

Back to my original question, do you see now what I meant by it?
Energy and work are not completely identical even though they use the same unit of measure.

From Work, Energy and Power

Work refers to an activity involving a force and movement in the directon of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work.

Energy is the capacity for doing work. You must have energy to accomplish work - it is like the "currency" for performing work. To do 100 joules of work, you must expend 100 joules of energy.
 

sram

Member
Energy and work are not completely identical even though they use the same unit of measure.

From Work, Energy and Power

Work refers to an activity involving a force and movement in the directon of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work.

Energy is the capacity for doing work. You must have energy to accomplish work - it is like the "currency" for performing work. To do 100 joules of work, you must expend 100 joules of energy.


So I can't say that the Potential from a to b, electric potential that is, is the energy per unit charge, associated with transporting said charge from a to b. This is what Claude Abraham wrote, I just replaced work with energy.
 

ke5frf

New Member
Shooooot! I actually meant to say the electric potential difference, not just the potential difference. Sorry I thought it was clear since It was posted here.

**broken link removed**

Back to my original question, do you see now what I meant by it?


Thanks.

It doesn't matter, that was the point of my post. Electrical potential difference is the equivelant of every other form of potential difference by laws of physics.

Work is a force acting upon or displacing an oject.
Work that is driven by electricity is the equivelant of work that is driven by compressed gases, thermal energy, or the gates of Hoover Dam.

Mr. Crutschow described the difference between energy and work.

But the point is, these definitions of work, energy, potential, force, horsepower, pressure, flow, resistance, capacity, etc are pretty universal in their application weather its electronics, mechanics, hydraulics, or pneumatics that we are discussing.

In almost all cases there is an equivelant and the metrics are proportional. In other words, there is an "ohm's law" for pneumatic systems that works the same way as electrical systems, even if the units are not the same.

Even if you look at the RC time constant of a capacitor and the 5 step rise/fall time on a graph, it equates to the response of a compressed air cylinder as it is filled to capacity with a gass through a resistive valve.

I'm off on a tangent, but you see now how these words all have their own meaning and aren't usually interchangeable.
 
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ke5frf

New Member
Also, energy is the ability to do work. Something can not have the ability to do itself (ehem)...except single celled organisms I suppose ;)

I actually think, your original definition is incorrect. ie "potential difference is the work needed to move one electrical charge from one point to another"...The word work is incorrect here, and energy would be a better word but still not technically correct.

This is because, (and I'm trying to explain this the best I can and might be slightly off)...Potential difference can be expressed as "potential energy" as well. Only, you have to realize that potential is the adjective here and qualifies the word energy. If energy has been released in the form of power, and no longer has potential, it is still energy.

I think it can be confusing. The other day I tried to explain the difference between voltage and charge, which is very much along these lines. A charge is a molecule or bunch of molecules under some state of excitement weather electrical, thermal, etc...if you follow. Voltage is potential to release the energy stored in those molecules. The charge represents the energy and voltage represents the pressure it is under...ie charges can be "compressed" metaphorically to exist in crowded conditions where they have more opportunity to be liberated. See what I mean? I know it is VERY confusing but man when you sorta get all of this it opens the floodgates of understanding, even things that you may or may not quite get in all phases of engineering or physics, even electrical.
 

sram

Member
Well, thanks ke5frf and everybody who contributed into this thread. So ke5frf, what would be the best definition of electric potential difference in your opinion?

Thanks.
 

ke5frf

New Member
It is very simple. Voltage difference! It is the potential that exists between one voltage source and another.

It is electromotive force. The force required to move electrons. A battery or generator is just like a pump. If you increase the size of the pump's diaghram or impeller you will generate more force and increase the pressure. In a generator, if you change the strength of the rotating DC electric field, you can increase the voltage or electromotive force, just like the pump.

Pumps can fill up a cylinder with gas and once the density of the gas molecules goes beyond an ambient level, the pressure will be said to increase and the gas will be said to be COMPRESSED. So it is storing that pressure, or force, and can be released and made to do work.

In a manner of speaking, a battery that is being charged is being filled with "compressed electrons"...Now don't get me wrong, this is not literal, but you might say that electric field strength is the equivelant of molecular density of a gas. If the field is stronger, it may be said to be "more dense". At least that is how my mind sees it without a lot of math and formulae.

Electrical pressure is potential difference.

Oh, another point though...potential difference does not have to be the voltage between positive supply and ground. It could be the difference between two positive supplies or even two negative supplies.

Someone correct me if I'm wrong, but did you know that you can run (many) electronic devices that require a 12 volt supply (customarily 12 volts vs ground potential) with two NEGATIVE power supplies....ie a -24 volt supply and a -12 volt supply would work. hook the -24 volts to the negative terminal and the -12 volts to the positive terminal and the device, in theory, will work. This is because a potential difference of 12 volts still exists which is the electomotive force required to make the device work.

I say in theory because I've never actually done this, but this is true as I understand it.
 

olly_k

Member
It is very simple. Voltage difference! It is the potential that exists between one voltage source and another.

It is electromotive force. The force required to move electrons. A battery or generator is just like a pump. If you increase the size of the pump's diaghram or impeller you will generate more force and increase the pressure. In a generator, if you change the strength of the rotating DC electric field, you can increase the voltage or electromotive force, just like the pump.

Pumps can fill up a cylinder with gas and once the density of the gas molecules goes beyond an ambient level, the pressure will be said to increase and the gas will be said to be COMPRESSED. So it is storing that pressure, or force, and can be released and made to do work.

In a manner of speaking, a battery that is being charged is being filled with "compressed electrons"...Now don't get me wrong, this is not literal, but you might say that electric field strength is the equivelant of molecular density of a gas. If the field is stronger, it may be said to be "more dense". At least that is how my mind sees it without a lot of math and formulae.

Electrical pressure is potential difference.

Oh, another point though...potential difference does not have to be the voltage between positive supply and ground. It could be the difference between two positive supplies or even two negative supplies.

Someone correct me if I'm wrong, but did you know that you can run (many) electronic devices that require a 12 volt supply (customarily 12 volts vs ground potential) with two NEGATIVE power supplies....ie a -24 volt supply and a -12 volt supply would work. hook the -24 volts to the negative terminal and the -12 volts to the positive terminal and the device, in theory, will work. This is because a potential difference of 12 volts still exists which is the electomotive force required to make the device work.

I say in theory because I've never actually done this, but this is true as I understand it.

Only if the two voltage rails share the same ground. I do this with a fan I have strapped to the back of my old SOny CRT (try to keep cool and prolong life :) ). I have the fan + connected to +12v and the negative to +5v. Fan is just the right speed and not overly noisy :)
 

sram

Member
It is very simple. Voltage difference! It is the potential that exists between one voltage source and another.

It is electromotive force. The force required to move electrons. A battery or generator is just like a pump. If you increase the size of the pump's diaghram or impeller you will generate more force and increase the pressure. In a generator, if you change the strength of the rotating DC electric field, you can increase the voltage or electromotive force, just like the pump.

Pumps can fill up a cylinder with gas and once the density of the gas molecules goes beyond an ambient level, the pressure will be said to increase and the gas will be said to be COMPRESSED. So it is storing that pressure, or force, and can be released and made to do work.

In a manner of speaking, a battery that is being charged is being filled with "compressed electrons"...Now don't get me wrong, this is not literal, but you might say that electric field strength is the equivelant of molecular density of a gas. If the field is stronger, it may be said to be "more dense". At least that is how my mind sees it without a lot of math and formulae.

Electrical pressure is potential difference.

Oh, another point though...potential difference does not have to be the voltage between positive supply and ground. It could be the difference between two positive supplies or even two negative supplies.

Someone correct me if I'm wrong, but did you know that you can run (many) electronic devices that require a 12 volt supply (customarily 12 volts vs ground potential) with two NEGATIVE power supplies....ie a -24 volt supply and a -12 volt supply would work. hook the -24 volts to the negative terminal and the -12 volts to the positive terminal and the device, in theory, will work. This is because a potential difference of 12 volts still exists which is the electomotive force required to make the device work.

I say in theory because I've never actually done this, but this is true as I understand it.

Hmm. I need a definition in terms of work/energy. Or force maybe. You can't just say electric potential difference is voltage difference. That's just like saying the same thing.

Thanks.
 

ke5frf

New Member
LOL that's because**it is** the same thing! Isn't that what a definition is????

I have given you tons of examples of work/energy, and force and how they relate, and so have a few others who posted. How much more clear can this be? I mean, I really want to help!

OK one more example, and I'll use an electric example.

You connect an electric AC motor to a generator. The generator creates power, which is voltage and current (pressure and flow). When the motor spins, we say that it has become energized...it is in a state of energy, having the capacity to do work. Some of that energy being released in the form of heat, some of it mechanical movement. And when the motor shaft actuates a belt which drives a conveyor (the load), we say that it is actually doing work. The torque and speed of the rotor as it reacts to the load (the belt) we will call force.

pressure, flow, work, force, energy, potential.

See how one concept is related to the next, yet they aren't the same?

I can't explain this any better. I'm beginning to think you are waiting for the answer that agrees with your original post, which isn't going to be the case!
 
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sram

Member
LOL that's because**it is** the same thing! Isn't that what a definition is????

I have given you tons of examples of work/energy, and force and how they relate, and so have a few others who posted. How much more clear can this be? I mean, I really want to help!

OK one more example, and I'll use an electric example.

You connect an electric AC motor to a generator. The generator creates power, which is voltage and current (pressure and flow). When the motor spins, we say that it has become energized...it is in a state of energy, having the capacity to do work. Some of that energy being released in the form of heat, some of it mechanical movement. And when the motor shaft actuates a belt which drives a conveyor (the load), we say that it is actually doing work. The torque and speed of the rotor as it reacts to the load (the belt) we will call force.

pressure, flow, work, force, energy, potential.

See how one concept is related to the next, yet they aren't the same?

I can't explain this any better. I'm beginning to think you are waiting for the answer that agrees with your original post, which isn't going to be the case!

No No, don't get me wrong. You actually already said what I want. The argument I had with somebody was whether

"the Potential from a to b, electric potential that is, is the energy per unit charge, associated with transporting said charge from a to b"

is a correct statement or not. I say it is correct, but he insists in using the word work instead of energy.

Remember, you actually supported my thinking when you said: "I actually think, your original definition is incorrect. ie "potential difference is the work needed to move one electrical charge from one point to another"...The word work is incorrect here, and energy would be a better word but still not technically correct"

I want to use this page to prove him wrong that's all.

And it is not about me understanding, I fully understand the difference as I'm an engineer myself. I just want somebody else ( I see this site as a very decent source of information and I highly respect its knowledgeable members) to support my thinking.


Anyways, I can't force you to post here anymore. I can't be more grateful to you. Thanks a million.

sram
 
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