Exploring the Effects of Connecting One Side of a Wire to a Battery

[Bassalisk]

When we connect a wire to a negative side of the battery, electrons flow from the negative terminal to the wire in order to make the electric potential same. That only happens for a short period.(the other side of the wire is loose)

Having said that, what would happen if we connect just one side of the wire to the positive side, like before?

I was told that positive charge would go to this wire, understandable... But is it more correct to say that the electron will flow from the wire to the positive side, making the wire positive?

 

[uart]

I was told that positive charge would go to this wire, understandable... But is it more correct to say that the electron will flow from the wire to the positive side, making the wire positive?

Yes that is more correct. But please bare in mind that before the wire is connected to the battery we do not actually know what it's initial potential is relative to the negative of the battery. Given that these two items are "floating" relative to each other the wire may in fact be significantly more positive than the battery +ive terminal before it's connected, so during charge equalization the current would then go the other way. Similarly the wire may initially be even more negative than the -ive terminal of the battery. Unless some specific initial conditions are set up on the wire's potential then in general we just don't know.

 

[Evil Bunny]

Yes that is more correct. But please bare in mind that before the wire is connected to the battery we do not actually know what it's initial potential is relative to the negative of the battery. Given that these two items are "floating" relative to each other the wire may in fact be significantly more positive than the battery +ive terminal before it's connected, so during charge equalization the current would then go the other way. Similarly the wire may initially be even more negative than the -ive terminal of the battery. Unless some specific initial conditions are set up on the wire's potential then in general we just don't know.

How would anything flow if there was not a complete circuit to the negative terminal?

To measure the potential between the (+) terminal and the wire would only require a voltmeter, correct? Would it be common to see anything other than 0V if you did that?

 

[dlgoff]

This sort of reminds me of this thread:

https://www.physicsforums.com/showthread.php?t=391171"

And in particular, this post:

https://www.physicsforums.com/showpost.php?p=2981666&postcount=13"

 

[uart]

How would anything flow if there was not a complete circuit to the negative terminal?

Capacitance. The OP was talking about a tiny brief discharge current.

To measure the potential between the (+) terminal and the wire would only require a voltmeter, correct? Would it be common to see anything other than 0V if you did that?

The electrostatic potential could be very much other than 0V between the wire and the battery -ive terminal.

 

[Bassalisk]

How would anything flow if there was not a complete circuit to the negative terminal?

To measure the potential between the (+) terminal and the wire would only require a voltmeter, correct? Would it be common to see anything other than 0V if you did that?

when u connect a wire to one terminal, depending on the state of the wire a micro charge will flow for a sec in order to make that wire same potential as that terminal

 

[Evil Bunny]

Let me see if I have this right... In a capacitor, the only way a charge can build up on the plate of a capacitor is if there is an equal charge on the other plate, holding it in place with the electric field, correct?

And a battery (or any other voltage source for that matter) can only "push" so many electrons to one side (ie, it can only produce X volts and no more whatsoever). If it were able to push even a single electron without accepting one on the other pole, this voltage will have been exceeded and we just violated... something... lol

Now back to this example... Capacitance is related to the size of "parallel plates" (for example) and the distance they are apart. This relationship only works if the distance is small compared to the plate sizes... otherwise this relationship falls apart, correct?

But we are saying here that there is still some capacitance between the (+) terminal with the wire attached and the (-) terminal (this has got to be extraordinarily small)... meaning that if a single electron entered the positive terminal from the wire, another electron had to have "surfaced" onto the (-) terminal to hold it in place.

Do I have it right?

 

[Evil Bunny]

The electrostatic potential could be very much other than 0V between the wire and the battery -ive terminal.

Very much?

I think if you walked around with a charged battery and a voltmeter and put one meter lead on one of the battery terminals and the other lead on anything else besides the other terminal, your meter would read 0 volts. Is this incorrect?

 

[Bassalisk]

Let me see if I have this right... In a capacitor, the only way a charge can build up on the plate of a capacitor is if there is an equal charge on the other plate, holding it in place with the electric field, correct?

And a battery (or any other voltage source for that matter) can only "push" so many electrons to one side (ie, it can only produce X volts and no more whatsoever). If it were able to push even a single electron without accepting one on the other pole, this voltage will have been exceeded and we just violated... something... lol

Now back to this example... Capacitance is related to the size of "parallel plates" (for example) and the distance they are apart. This relationship only works if the distance is small compared to the plate sizes... otherwise this relationship falls apart, correct?

But we are saying here that there is still some capacitance between the (+) terminal with the wire attached and the (-) terminal (this has got to be extraordinarily small)... meaning that if a single electron entered the positive terminal from the wire, another electron had to have "surfaced" onto the (-) terminal to hold it in place.

Do I have it right?

Battery will "push" positive or negative charge, depending on the side of the terminal that the wire is connected until wire is the same potential as the terminal, if wire was on higher potential than the terminal then charge would imo rush from wire to the terminal (system will do everything to make it in equilibrium). Having both wires, ergo both plates on the same potential as the terminals, electric field kicks in since u have a large surface with lots of charge and those charges, how can i put this right... Pull each other and hold them in place.


Current will run only until both plates are on the same potential as the battery, provided that u have stable voltage battery. This process is called i think charging the capacitor.

 

[uart]

Very much?

I think if you walked around with a charged battery and a voltmeter and put one meter lead on one of the battery terminals and the other lead on anything else besides the other terminal, your meter would read 0 volts. Is this incorrect?

Depends on the voltmeter. If it's an electrostatic voltmeter then you're incorrect. A typical voltmeter with say 10 mega-ohm input resistance on the other hand will of course discharge electrostatic potential. That however is a measurement artifact.

Electrostatic potentials can be many thousands of volts and the voltage of the -ive terminal of a floating battery (not connected to anything else) has got nothing to do with it. Even just a floating wire that is high impedance with respect to Earth will usually pick up tens of volts from just the stray electric fields in the room. Try it with an oscilloscope probe some time. Without touching the ground clip stick a finger on the probe tip and you'll typically see ten's of volts of 60 Hz AC. And that's just pick up on a high impedance input, electrostatic voltages on "floating" objects can be much higher.

 

[uart]

Battery will "push" positive or negative charge, depending on the side of the terminal that the wire is connected until wire is the same potential as the terminal, if wire was on higher potential than the terminal then charge would imo rush from wire to the

Yep Bassalisk that's true. But please also understand the point I was trying to make which is that if the wire is initially floating (not connected in any way) with respect to the battery then we have zero information about the initial potential of the wire relative to either terminal of the battery.

 

[Bassalisk]

Yep Bassalisk that's true. But please also understand the point I was trying to make which is that if the wire is initially floating (not connected in any way) with respect to the battery then we have zero information about the initial potential of the wire relative to either terminal of the battery.

Yea true we don't know in which direction the equilibration will happen, or whether will be a need for it anyway, maybe the wire was already on that same potential as the terminal, i got it now ^^.