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Capacitor

Faybull

Well-Known Member
Okay, you discharge a capacitor, and weigh it...then,
You charge the capacitor, and weigh it.
Is the weight the same?
 

DawudTalut

Peace be upon you.
Electrons shift the plate.

"No, it is the same weight. When a capacitor is uncharged, the number of electrons is equal on both sides of the capacitor. When a capacitor is charged, the electrons on the positive side of the capacitor leave and go to the negative side of the capacitor (while they aren't actually the exact same electrons, you can think of it like that). Therefore, the capacitor's weight stays the same."
Is a capacitor heavier when charged?
 

Avi1001

reform Jew humanist liberal feminist entrepreneur
Electrons shift the plate.

"No, it is the same weight. When a capacitor is uncharged, the number of electrons is equal on both sides of the capacitor. When a capacitor is charged, the electrons on the positive side of the capacitor leave and go to the negative side of the capacitor (while they aren't actually the exact same electrons, you can think of it like that). Therefore, the capacitor's weight stays the same."
Is a capacitor heavier when charged?
Dawad, read the 2nd reply. It indicates that it is a function of the materials used...:D
 

BSM1

What? Me worry?
It would be different on an incredibly sensitive scale.

Do we assume that the actual charge has mass or weight? Or that electrons are actually ejected in the discharge? If this is the case wouldn't the capacitor have to replenish its store of electrons to stay viable?
 

Parsimony

Well-Known Member
I admit that I do not know much about the operation of capacitors. If a charged capacitor contains the same number of particles as an uncharged capacitor, but contains more energy, then it would indeed weigh very slightly more (due to matter-energy equivalence). Picking a rock up off of the ground would make the rock heavier for the same reason (increased gravitational potential energy).
 

Shadow Wolf

Certified People sTabber
Just the "added" weight of the charge to the electron would technically add some weight, but unless you're doing chemistry down to the atomic weight or quantum physics I don't see this weight causing any noticeable, practical, or real differences. No different than picking up a fully charged battery or a dead battery.
 

Sultan Of Swing

Well-Known Member
Okay, you discharge a capacitor, and weigh it...then,
You charge the capacitor, and weigh it.
Is the weight the same?
Eh, good question.

When a capacitor is charged, an electric field is induced between the two capacitor plates across the insulating dielectric. Technically, there is now a voltage across these two plates, and stored energy. I would say the charged capacitor is then negligibly heavier due to the energy stored by the electric field. I would also think that there would be a greater concentration of charge carriers in the capacitor plates than in the rest of the circuit, thereby implying a higher mass of the capacitor itself. I am not aware of any scale we have available to us that could actually measure the difference.
 

Wirey

Fartist
According to convential current flow theory there would be no change in weight. As electrons piled onto the chaged plate (-), they would be drawn from the other plate in the capacitor (+), leaving 'holes'. At discharge, those electrons would flow back to their holes, creating a situation where there is no alteration in overall electron content between the two plates taken as a whole. As convential current flow theory is the basis of all solid state theory, it is plain to see that a charged capacitor will weigh the same at any state of charge. Anyone who disagrees with this obviously has no concept of electrical theory, says the guy who works as an electrical engineer and once built a functional lie detector as a school project. So nyah!

EDIT: Before you bother proving you're a moron by arguing with me, go read about the P-N junction.
 

Sultan Of Swing

Well-Known Member
According to convential current flow theory there would be no change in weight. As electrons piled onto the chaged plate (-), they would be drawn from the other plate in the capacitor (+), leaving 'holes'. At discharge, those electrons would flow back to their holes, creating a situation where there is no alteration in overall electron content between the two plates taken as a whole. As convential current flow theory is the basis of all solid state theory, it is plain to see that a charged capacitor will weigh the same at any state of charge. Anyone who disagrees with this obviously has no concept of electrical theory, says the guy who works as an electrical engineer and once built a functional lie detector as a school project. So nyah!

EDIT: Before you bother proving you're a moron by arguing with me, go read about the P-N junction.
I am going to risk proving I'm a moron. :D

When the capacitor discharges, what happens to all the charge carriers that have piled up on one side? Didn't they come from the rest of the circuit? Do they not return to a net even spread across the circuit rather than around the capacitor?

EDIT: I mean, the charge carriers that would attract the other side in the first place, not the ones attracted from the other side leaving behind the holes
 

Sultan Of Swing

Well-Known Member
And oi oi, I thought P-N junctions were used for diodes and transistors (NPN PNP), wasn't aware the same principle worked with capacitors.
 

Sultan Of Swing

Well-Known Member
Oh dangit you're right, Wirey, the net charge remains the same, the charge carriers would repel the same number the other side to form the holes.

I won't edit my previous posts so the world can recognise my moronity.

Althouuuugh, while the net charge remains the same, there is stored energy in a charged capacitor, and not in a discharged one... wouldn't that affect the mass in some clever Einsteiny way?
 

Wirey

Fartist
Oh dangit you're right, Wirey, the net charge remains the same, the charge carriers would repel the same number the other side to form the holes.

I won't edit my previous posts so the world can recognise my moronity.

Althouuuugh, while the net charge remains the same, there is stored energy in a charged capacitor, and not in a discharged one... wouldn't that affect the mass in some clever Einsteiny way?

Nope. It's not stored energy, it's unbalanced energy. A battery contains stored energy. And I believe the correct term is moronipity.
 

Wirey

Fartist
And oi oi, I thought P-N junctions were used for diodes and transistors (NPN PNP), wasn't aware the same principle worked with capacitors.

I was referring to behaviour of electrons, not construction. The P-N junction is a hole/electron rich barrier with a net neutral charge.
 

chlotilde

Madame Curie
Okay, you discharge a capacitor, and weigh it...then,
You charge the capacitor, and weigh it.
Is the weight the same?
There is a little rule called conservation of Mass and another called m=E/c^2.
I know of no capacitor that could accept a charge greater than the speed of light factor to make a measurable change in mass.
 
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