Electric Potential: Explaining Differences

[MIA6]

I am so confused with 'electric potential energy', 'electric potential' and 'potential difference'?! What's their difference? The first one is an energy, the second one is a work? How about the third one? Hope you can explain to me, thanks so much.

 

[Dick]

Energy is the same as work. If you change the last one to 'electric potential difference' (as opposed to say, 'gravitational potential difference') they are all the same concept. The last one simply refers to a 'difference' of potential between two points, of course the first two are also implicitly differences between the potential at some point and an arbitrary fixed reference point. There is no notion of a potential independent of reference to some other point. So really, they are all the same.

 

[Mindscrape]

To an extent they are all the same. Electric potential energy and electric potential, which really are the same because often people just drop the energy part of the name, you can think of as the electrical version of gravitation potential. The gradient of the potential, the rate of change of the potential in all dimensions, gives the electric field.

Potential difference is what you are thinking about with work. It is described as the amount of work it would take for a charge to move from one spot to another under a given force. Work is the integral of a force dotted with a displacement vector over a curve, or path, that the object follows. Work energy theorem says that the amount of energy transferred in a system equals the work done.

They are all related to one another in the general concept of potential energy. Try this helpful link:

http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html#pe

 

[MIA6]

My book seems to talk about electric potential as a work, is that okay?

 

[Dick]

Technically, it is work (or energy) per unit charge. Moving 2C of charge through the same potential difference as 1C involves twice the work.

 

[learningphysics]

Electric potential energy is not the same as electric potential... they are related, but you shouldn't think of them as the same...

electric potential*charge gives electric potential energy...

Suppose you have a charge q1... the potential due to that charge a distance r away is kq1/r. If you place another charge q2, at that point r then the energy between the two is kq1q2/r. So potential is Energy/charge... similar to how electric field strength = Force/charge

The potential difference is just the potential at one point - the potential at the other...

If two points have a potential difference V... that means that a charge q will gain q*V in potential energy by going from the point of lower potential to the point of higher potential...

Potential = energy/unit charge... Field = force/unit charge

 

[MIA6]

okay, I got it. Is a neutral object who contains equal amounts of positive and negative charge a charged object? Or a charged object must have different amounts of positive and negative charges, as in different numbers of electrons and protons.

 

[rootX]

okay, I got it. Is a neutral object who contains equal amounts of positive and negative charge a charged object?

no, it's only charged when it has excess or deficiency of electrons.

 

[MIA6]

thanks for your guys' replies.

 

[rootX]

It depends on the valence electrons.

So, metallic object would move away from the charged object.

 

[MIA6]

It depends on the valence electrons.

So, metallic object would move away from the charged object.

I thought a neutral object would redistribute the electrons and protons inside, so it will usually first attract to the charged object. Here is a question about induction, If the object is then disconnected from the ground while the positively charged rod is nearby, the object is left with a net negative charge. What does that mean by left with a net negative charge.

 

[rootX]

I thought a neutral object would redistribute the electrons and protons inside, so it will usually first attract to the charged object. Here is a question about induction, If the object is then disconnected from the ground while the positively charged rod is nearby, the object is left with a net negative charge. What does that mean by left with a net negative charge.

But all neutral objects are not capable of doing so.[non-conductors]

So, the positive rod would pull all electrons to one side leaving the other side positive. And the ground has plenty of electrons that are attracted by that positive side of the object...
and so in the end the object would be negatively charged.

 

[learningphysics]

I thought a neutral object would redistribute the electrons and protons inside, so it will usually first attract to the charged object. Here is a question about induction, If the object is then disconnected from the ground while the positively charged rod is nearby, the object is left with a net negative charge. What does that mean by left with a net negative charge.

Have a look at the animation in the middle of this page:

http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/estatics/isop.html

It shows this exact process, except leaving a net positive charge on the object instead of negative.

 

[MIA6]

But all neutral objects are not capable of doing so.[non-conductors]

So, the positive rod would pull all electrons to one side leaving the other side positive. And the ground has plenty of electrons that are attracted by that positive side of the object...
and so in the end the object would be negatively charged.

Is pith ball a conductor or not? Since it was written on my book that it rearrange its electrons and protons. If electrons from ground/earth attract to the positive side of the object, then the protons in the positive side will go into the ground? but it is disconnected? Does net negative charge or net positive charge means that an object has more electrons than protons; an object has more protons than electrons?

 

[rootX]

=I think it's a conductor then.
=protons don't move :)
=negative charge = excess of electrons

 

[MIA6]

=protons don't move :)

Then how come you said that the ground has plenty of electrons that are attracted by that positive side of the object...
and so in the end the object would be negatively charged.
If the object changes from neutral to negatively charged and disconnected to the ground, where do other protons go?

 

[rootX]

Then how come you said that the ground has plenty of electrons that are attracted by that positive side of the object...
and so in the end the object would be negatively charged.
If the object changes from neutral to negatively charged and disconnected to the ground, where do other protons go?

protons just stay there.
the object gets more electrons, so in other words, the object's mass would be increased slightly.

 

[MIA6]

so the object gets more electrons from the ground? but it's disconnected.

 

[rootX]

so the object gets more electrons from the ground? but it's disconnected.

yes, if there's a contact.
oops, I missed that part.
So, the object can get electrons from the ground only if there's a contact.

 

[MIA6]

But on my book, it says If the object is then disconnected from the ground while the positively charged rod is nearby, the object is left with a net negative charge. Well, of course this is a neutral object. So it means electrons are more than protons eventually, but how come? If it is disconnected from the ground, then there is no way to gain electrons.

 

[learningphysics]

But on my book, it says If the object is then disconnected from the ground while the positively charged rod is nearby, the object is left with a net negative charge. Well, of course this is a neutral object. So it means electrons are more than protons eventually, but how come? If it is disconnected from the ground, then there is no way to gain electrons.

While the ground is connected, and the positively charged rod remains nearby... the conductor has a net negative charge, and when the ground is disconnected it stays that way...

If there was never any ground connection, then when the rod is brought nearby, electrons from one part of the conductor leave and accumulate near to where the rod is... so electrons are depleted from one region (leaving it positive)... and accumulate in the region near the rod (leaving that region negative). but the entire conductor is still neutral... then connecting a ground means that electrons will come up from the ground and fill up the region that is positive... so now there is a net negative charge on the conductor... it is grounding that allows the net negative charge to accumulate...

Did you watch the animation?

 

[MIA6]

While the ground is connected, and the positively charged rod remains nearby... the conductor has a net negative charge, and when the ground is disconnected it stays that way...

If there was never any ground connection, then when the rod is brought nearby, electrons from one part of the conductor leave and accumulate near to where the rod is... so electrons are depleted from one region (leaving it positive)... and accumulate in the region near the rod (leaving that region negative). but the entire conductor is still neutral... then connecting a ground means that electrons will come up from the ground and fill up the region that is positive... so now there is a net negative charge on the conductor... it is grounding that allows the net negative charge to accumulate...

Did you watch the animation?

Oh, I reread my book, it means to disconnect with the ground after having connected with the ground. Yes, I have. Thanks a lot.