Will a Glass Ball Discharge in an Insulator?

  • Thread starter Steven Ellet
  • Start date
  • Tags
    Discharge
In summary: Berkeman. If the sphere is totally isolated from anything else, the extra electrons will not move around.
  • #1
Steven Ellet
85
3
For example, if I negative charge a glass ball and put it into a rubber (or any insulator) case to shield it from being grounded, will it discharge on its own? I know that a capacitor will discharge with time( assuming that there is no input.)
 
Engineering news on Phys.org
  • #2
Steven Ellet said:
For example, if I negative charge a glass ball and put it into a rubber (or any insulator) case to shield it from being grounded, will it discharge on its own? I know that a capacitor will discharge with time( assuming that there is no input.)

Welcome to the PF.

That comes down to leakage current mechanisms. With capacitors, there is some leakage current spec associated with each type of capacitor (check their datasheets for the numbers).

For other geometries, the leakage current mechanisms will be different. You can certainly come up with some situations where the leakage current is very low, like for an object in space, for example. Such an object will stay charged up for a very long time.
 
  • #3
The insulated container your negative charged sphere is placed in is a dielectric material.
The charge on the surface of your sphere will attract positive charge to the inside surface of the insulator and so make the outside of the insulator less positive = negative. This is probably best considered as a problem of electrostatics, capacitance in series.
 
  • #4
Please clarify

Berkeman, you mentioned "current mechanisms" which, in my mind, implies that the spare electrons that are gathered on the glass ball are moving more than the average electron which are already in the ball making the spare electrons electricity rather than just spare electrons, however, I was under the impression that in a charge object, the spare electrons don't move more than a normal electron without an outside force, am i wrong?
 
  • #5
Steven Ellet said:
Berkeman, you mentioned "current mechanisms" which, in my mind, implies that the spare electrons that are gathered on the glass ball are moving more than the average electron which are already in the ball making the spare electrons electricity rather than just spare electrons, however, I was under the impression that in a charge object, the spare electrons don't move more than a normal electron without an outside force, am i wrong?

You missed the important word when you quoted berkeman he said Leakage current mechanisms.
I think you will find he is referring to the different ways a current/charge will leak from a charged surface. Think of say .. a capacitor .. .it has 2 parallel plates with a dielectric in between them. But no dielectric is a perfect insulator ... so the leakage mechanism there will be through the dielectric till the charge is balanced in both plates

There will be a "slow" discharge of your glass sphere into the rubber or other material that its sitting in.

on charged sphere ... the charge will be evenly distributed across the surface of the sphere

cheers
Dave
 
  • #6
davenn the reason I left out leakage is because that was not my point. My point was do extra electrons have a current? If they have a current, then I expect it to discharge, but if there is no current will it still discharge?
 
  • #7
it is the point :smile:

electrons DONT have a current
the movement of electrons is a current or moving charge

as hinted at earlier, if the glass sphere is totally isolated from anything else then any charge on the sphere be it positive or negative will spread out evenly over the sphere and remain there

And also as said earlier ... any contact with other material WILL cause leakage ( a small flow of current/charge) will, if left long enough, eventually find a balance of charge remaining on the sphere ( any other charged object)

Dave
 
  • #8
Thank you

That is all I wanted to know, thank you. :approve:
 
  • #9
If the distance between the ball and the insulating case is microscopically small all around the ball it may stay charged for years since such a thin layer of air is an incredibly good insulator in contrast to thick layers of air which are only moderately good insulators.
 
  • #10
DrZoidberg said:
If the distance between the ball and the insulating case is microscopically small all around the ball it may stay charged for years since such a thin layer of air is an incredibly good insulator in contrast to thick layers of air which are only moderately good insulators.

Interesting. Why is that?
 
  • #11
Maybe, if leakage is the result of ionising radiation reacting with the mass of air. Less air is less collisions, so less ions produced = lower leakage ? ? ?
 
  • #12
There are two effects here.
For once the breakdown strenght of air increases as the gap width decreases. That is predicted by Paschen's law
http://en.wikipedia.org/wiki/Paschen's_law
At a few µm you need more than 40 MV/m while for a gap between 1cm and 1m it's around 3MV/m.
The second effect was explained already by Baluncore. There are not many ions in a tiny air gap so you can't get much of a current.
It's actually possible to "glue" two pieces of plastic foil together with static charge and under the right conditions (no moisture in between the foils, smooth surface so the gap is really small) the foil will stick together for many years.
You probably know that a roll of plastic foil can become charged when it's unrolled. But most people don't realize that that charge was put on the foil in the factory. It's not produced when you unroll it. Equal amounts of positive and negative charge are trapped in the roll of foil causing very strong fields in the gaps between the layers, while the total net charge is zero. That roll can be sitting on a shelf for years without loosing it's charge.
 
  • #13
Very interesting. Thanks! :smile
 
  • #14
DrZoidberg said:
There are two effects here.
For once the breakdown strenght of air increases as the gap width decreases. That is predicted by Paschen's law
http://en.wikipedia.org/wiki/Paschen's_law
At a few µm you need more than 40 MV/m while for a gap between 1cm and 1m it's around 3MV/m.
The second effect was explained already by Baluncore. There are not many ions in a tiny air gap so you can't get much of a current.
It's actually possible to "glue" two pieces of plastic foil together with static charge and under the right conditions (no moisture in between the foils, smooth surface so the gap is really small) the foil will stick together for many years.
You probably know that a roll of plastic foil can become charged when it's unrolled. But most people don't realize that that charge was put on the foil in the factory. It's not produced when you unroll it. Equal amounts of positive and negative charge are trapped in the roll of foil causing very strong fields in the gaps between the layers, while the total net charge is zero. That roll can be sitting on a shelf for years without loosing it's charge.
Interesting DrZoidberg, but how would one know if there was the right level of air in between the material? or what the right level of air is?
 
  • #15
It doesn't need to be precise. You just need two smooth surfaces that touch each other, at least one of which should be a good insulator, the other one can either be insulating or conducting e.g. aluminum and polyethylen foil. Even though they appear to touch there really is a microscopically small gap over most of the area.
 
  • Like
Likes 1 person

1. How does a glass ball discharge in an insulator?

A glass ball can discharge in an insulator through a process called triboelectrification. This occurs when two materials come into contact and transfer electrons, resulting in one material becoming positively charged and the other becoming negatively charged. In the case of a glass ball and an insulator, the glass ball can become negatively charged and discharge its excess electrons into the insulator.

2. What materials are commonly used for insulators in this experiment?

Commonly used insulators in this experiment include rubber, plastic, and glass. These materials have high resistivity, meaning they do not allow electrons to flow easily, making them effective insulators.

3. How does the size of the glass ball affect its discharge in an insulator?

The size of the glass ball can affect its discharge in an insulator. A larger glass ball will have a greater surface area, allowing it to come into contact with more of the insulator and potentially transfer more electrons. However, the overall charge of the glass ball will also play a role in its discharge, so size is not the only determining factor.

4. Can the type of insulator used affect the discharge of a glass ball?

Yes, the type of insulator used can affect the discharge of a glass ball. Different insulators have different levels of resistivity, which can impact the flow of electrons. Additionally, the surface properties of the insulator can also play a role in the transfer of electrons between the glass ball and the insulator.

5. What is the significance of this experiment in the field of electricity and energy?

This experiment can help us understand the concept of static electricity and the behavior of insulators and conductors. It also has practical applications in industries such as electronics and energy production, as understanding the properties of insulators is crucial in preventing electrical malfunctions and ensuring safe energy production and transmission.

Similar threads

Replies
4
Views
759
Replies
2
Views
758
  • Electrical Engineering
Replies
14
Views
2K
Replies
8
Views
662
  • Electrical Engineering
Replies
1
Views
1K
Replies
10
Views
1K
  • Electrical Engineering
Replies
4
Views
1K
  • Electrical Engineering
Replies
5
Views
1K
Replies
8
Views
857
  • Electromagnetism
Replies
7
Views
851
Back
Top