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NothingCrushesUs
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Hiya everyone,

can anyone tell me what 'absolute electric potential' actually means?

thanks,
NothingCrushesUs
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Stonebridge
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(Original post by NothingCrushesUs)
Hiya everyone,

can anyone tell me what 'absolute electric potential' actually means?

thanks,
NothingCrushesUs
The term can be used to describe the quantity V in the formula

V = \frac{1}{4\pi\epsilon_0}\frac{Q}{r}

where V is the (absolute) electrical potential at a point a distance r from a charge Q
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NothingCrushesUs
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(Original post by Stonebridge)
The term can be used to describe the quantity V in the formula

V = \frac{1}{4\pi\epsilon_0}\frac{Q}{r}

where V is the potential at a point a distance r from a charge Q
:P I understand what electric potential is, I just have no idea what saying 'absolute' before it does to it :P Thanks nonetheless though, although if you have any idea about the absolute thing, I'd be very appreciative
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Stonebridge
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(Original post by NothingCrushesUs)
:P I understand what electric potential is, I just have no idea what saying 'absolute' before it does to it :P Thanks nonetheless though :P
It means it's not relative.

You can move a charge around in an electric field and measure its change in potential in volts. You can arbitrarily assign a value to a potential at a point and measure the change that occurs between one point and another.
For example you can have a potential of 500V on one plate of a capacitor and 100V on the other. It doesn't actually matter what those potentials are, but the difference is 400V
The potentials on the plates are not absolute.
A similar thing happens with gravity. You can take the zero locally to be anywhere. The key idea is the potential difference between points.

In the formula I gave - that is the absolute potential at a point. Not relative to any other potential.
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NothingCrushesUs
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(Original post by Stonebridge)
It means it's not relative.

You can move a charge around in an electric field and measure its change in potential in volts. You can arbitrarily assign a value to a potential at a point and measure the change that occurs between one point and another.
For example you can have a potential of 500V on one plate of a capacitor and 100V on the other. It doesn't actually matter what those potentials are, but the difference is 400V
The potentials on the plates are not absolute.
A similar thing happens with gravity. You can take the zero locally to be anywhere. The key idea is the potential difference between points.

In the formula I gave - that is the absolute potential at a point. Not relative to any other potential.
Ah okay, so by saying it's absolute, you are effectively saying that by replacing dV and dr (which would make it relative) with just V and just r, you make it absolute?
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Stonebridge
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(Original post by NothingCrushesUs)
Ah okay, so by saying it's absolute, you are effectively saying that by replacing dV and dr (which would make it relative) with just V and just r, you make it absolute?
The potential in the formula I gave has always been "absolute". It's just that the word "absolute" is understood and not usually included.
Absolute just means that its value is determined by definition. (In this case with the zero being at infinity)
The same applies to (absolute) gravitational potential.
In the gravitational case, it distinguishes it from the mgh formula where you could take the local potential to be zero on the ground, for example. That would not be an absolute potential.
It's not unlike temperatures on the Kelvin scale being called absolute because they have a defined zero.
Do you have a problem with absolute temperature?

Other absolutes are
absolute magnitude (of a star) as opposed to apparent magnitude. (brightness)
absolute humidity of air (as opposed to relative humidity)

In all cases, the word absolute refers to the fact that the quantity is not measured with reference to the value of something else.

It probably isn't worth getting too worried about it.
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Scipio90
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(Original post by Stonebridge)
In the formula I gave - that is the absolute potential at a point. Not relative to any other potential.
Implicitly it's defined relative to V at infinity, which has been set to zero - surely an absolute potential makes no sense, since there's an underlying gauge freedom to electromagnetism.

I would suggest that without further context, "absolute potential" probably means |V|.
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Farhan.Hanif93
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(Original post by Scipio90)
Implicitly it's defined relative to V at infinity, which has been set to zero - surely an absolute potential makes no sense, since there's an underlying gauge freedom to electromagnetism.

I would suggest that without further context, "absolute potential" probably means |V|.
I agree with this.
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Stonebridge
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(Original post by Scipio90)
Implicitly it's defined relative to V at infinity, which has been set to zero - surely an absolute potential makes no sense, since there's an underlying gauge freedom to electromagnetism.

I would suggest that without further context, "absolute potential" probably means |V|.
It could well be, but the context, as far as I can make out, is of an A-Level student at school. If he returns to the thread, you will undoubtedly need to explain what |V| is.
I presume the OP has an A Level question or book somewhere that has used this term. In which case it's almost certain this is what it's referring to.

I would be happy for more context. Let's see if we get any.

Lack of context in questions on here is a constant source of unnecessary explanatory effort.
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NothingCrushesUs
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(Original post by Stonebridge)
It could well be, but the context, as far as I can make out, is of an A-Level student at school. If he returns to the thread, you will undoubtedly need to explain what |V| is.
I presume the OP has an A Level question or book somewhere that has used this term. In which case it's almost certain this is what it's referring to.

I would be happy for more context. Let's see if we get any.

Lack of context in questions on here is a constant source of unnecessary explanatory effort.
Yup, you presumed correctly It's in the AQA specification just for the record. Your explanations were perfect Thanks once again
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Stonebridge
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(Original post by NothingCrushesUs)
Yup, you presumed correctly It's in the AQA specification just for the record. Your explanations were perfect Thanks once again
Thanks. We usually get there in the end.
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930millionvolts
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I can explain what absolute electrical potential means. Take two electrodes, let one be the anode and the other be the cathode, now create a charge difference by moving some electrons from the anode to the cathode, then imagine taking this to the absolute limit, so all the electrons are on the cathode and all the protons are on the anode, then separate the electrodes to infinity. What you have now created is effectively
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have
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(Original post by 930millionvolts)
I can explain what absolute electrical potential means. Take two electrodes, let one be the anode and the other be the cathode, now create a charge difference by moving some electrons from the anode to the cathode, then imagine taking this to the absolute limit, so all the electrons are on the cathode and all the protons are on the anode, then separate the electrodes to infinity. What you have now created is effectively
Madam, please. It's thread from 2011
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Jzahra
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It is the work done in moving a unit positive charge from infinity to that point against electric field intensity keeping electrostatic equilibrium
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Eimmanuel
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(Original post by Jzahra)
It is the work done in moving a unit positive charge from infinity to that point against electric field intensity keeping electrostatic equilibrium
If you like to help, it would be better that you help on recent thread rather than an old thread that dated 2011.
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