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Is it possible to construct a portable ground using an + charged electret?

  1. Jul 22, 2012 #1
    Is it possible to construct a portable ground using an positively charged electret?

    I think it would be useful to a have an electrical ground that you can move with you anywhere, so that way no matter how powerful a device is, you could use it on the go without risking electrocution.

    Is it physically possible? How close are we technologically for making this?
     
  2. jcsd
  3. Jul 22, 2012 #2
    Can you provide a more detailed description of how you think this device would work?

    Sounds like you may be misunderstanding how grounding provides electrical safety.
     
  4. Jul 22, 2012 #3
    Electrons flow from negative to positive. Electrons at the (-) have a higher potential, and electrons at the (+) have a lower potential. As long as the electrons find their way to the +, then the electrons would not leave it as long as the potential there is lower than in the surroundings. I'm not sure if helps to be very vague and unspecific as to how I am misunderstanding how grounding provides electrical safety. I know I don't have full knowledge of the whys of how electrical safety works at all levels, but what did you mean specifically? Thanks in advance.
     
    Last edited: Jul 22, 2012
  5. Jul 22, 2012 #4

    Dale

    Staff: Mentor

    In the above I think that you mean potential energy, not potential. They differ by the charge, which is negative in the case of an electron.

    This would not be an effective ground. If a grounded human got in the loop then electrons would go from the ground through the human to your + terminal. The same EMF that moves electrons from the - terminal through a wire to the + terminal will gladly move electrons from the earth through a human to the + terminal.
     
  6. Jul 22, 2012 #5
    I really do mean potential, in the sense that that potential difference between a - and + terminal exists (i.e. potential energy per charge), causing the electron to decrease in potential as it goes from - to +.

    I'm not sure if the EMF would actually be the same. I would think that the EMF from the ground to the + terminal would be less than that from the - to the + terminal, so as long as the EMF is higher at the - terminal than the ground.

    I guess is what I want to ask is if whether or not a + charged electret can make a better "ground" than the earth itself.
     
    Last edited: Jul 22, 2012
  7. Jul 22, 2012 #6

    Dale

    Staff: Mentor

    Then you have it backwards. An electron increases in potential as it goes from - to +. It decreases in potential energy, and increases in potential.

    If the circuit isn't grounded somewhere (in the usual sense) then you cannot guarantee that.


    No, it would be significantly more dangerous.
     
  8. Jul 22, 2012 #7
    A negative charge has a negative potential surrounding it, while a positive charge has a positive potential surrounding it. Do you disagree with that?

    Negative charge multiplied by negative potential gives us a positive potential energy.
    Negative charge multiplied by positive potential gives us a negative potential energy.
    So if a negative charged moved from the negative potential (i.e. negative terminal) to the positive potential (i.e. positive terminal), then the result should be a negative change in potential energy, converting it into kinetic energy and higher-order electromagnetic energy components.

    I'm not sure how you think that I misunderstood that.

    I'm not talking about guarantees. Also, I'm quite sure that if the ground weren't at lower potential than the circuit, then it would not be a good ground whatsoever, and it would not act as such.

    Is there something magical about the Earth that makes it a better ground? NO. So please explain why man cannot make a better ground than the Earth is, unless you want to change your mind and say that it is possible for man to create a superior, artificial ground.
     
    Last edited: Jul 22, 2012
  9. Jul 22, 2012 #8
    From what I understood, the word potential should be analogous to potential energy divided by absolute charge.

    Unfortunately, it seems that electrons flowing from (-) to (+), which is in the direction of decreasing electrical potential energy per electron is in fact increasing electrical potential energy per charge (i.e. increasing potential) because the electron charge is negative. That is HORRIBLE nomenclature in my opinion.

    I wonder why they don't make it simple, such that a charge will flow from a higher potential to a lower one, regardless of its sign. So a (-) potential can be thought of as a "higher" potential for a negative charge and "lower" potential for a positive charge.

    Higher and lower do not mean positive and negative, as far as I understand these terms.
     
  10. Jul 22, 2012 #9

    Drakkith

    User Avatar

    Staff: Mentor

    An electrical ground protects people by providing a path for current to flow in the event of a fault. If a short develops the circuit immediately discharges through it's ground connection and trips a breaker or fuse. Note that by "ground" I mean the connection from the electronic device, not an earth connection. I believe the ground is usually connected to the chassis of the device so that if a short develops the current can return to the source through the chassis. This ground also serves as a convenient point to measure electric potential against, since the ground should always be neutral. Without a ground, shorts may not trip the breaker or fuse until someone comes into contact with the device and completes the circuit with themselves.

    Your device would NOT be a ground. It would be one side of a capacitor and would immediately discharge upon contact with a circuit, person, or other object if the voltage was high enough. This would be bad.
     
  11. Jul 22, 2012 #10

    Dale

    Staff: Mentor

    This is correct. It is in direct contradiction to what you said here:
    and here:
     
  12. Jul 22, 2012 #11

    Dale

    Staff: Mentor

    I never made any general claims that man couldn't make a better safety device than grounding to the Earth, just that this particular proposal isn't better.
     
    Last edited: Jul 22, 2012
  13. Jul 22, 2012 #12
    So in general, a positive electret would not be like an "electrical sponge soaking up electrons", but rather a place the electrons would be squished into, and would discharge in a way analogous to how a capacitor would be breached when the breakdown voltage was exceeded?

    If it is not possible to generate a portable ground using a positively charged electret, is there some way in general for a chassis to be designed to act as a very good ground for its size, or is size the only way to control this? What properties of chassis make it a good ground? Is there a way to improve on upon these properties in a very extreme way using some kind of special material?

    Or maybe the question I want to really ask is if there is a device that is to electrons in the same way that a sponge is to water, in that once the electrons are "absorbed" they have a tendency to stay there until they are "squeezed" out by external work applied to it in some way?
     
  14. Jul 23, 2012 #13
    Do you even know what I am talking about when I mention a positively-charged electret, as opposed to what Drakkith apparently thought I was talking about (i.e. his idea that I was talking about something comparable to a "positive" plate, like that on a capacitor, which itself is not necessarily a positive-charge, but simply of different "higher" potential than the negative side)? I'm asking because, normally, I don't accept the answer unless if I'm clear that my question was actually understood. That's all.
     
  15. Jul 23, 2012 #14

    Dale

    Staff: Mentor

    Yes, I understand what an electret is, as well as the similarities and differences between electrets and capacitors.
     
  16. Jul 23, 2012 #15
    What you describe seems to make certain assumptions about how the -, the +, the ground, and the human are connected with each other.

    Let's say a person was holding an insulated wire on end, connected to a grounding rod. The electricity would prefer to take the path of the grounding rod of course, assuming it is connected to earth. What I want to know is if instead of planting the rod on the ground, one instead had a positive electret in place of the grounding rod, so for example, electricity could prefer to flow to this + terminal instead of having to go to the Earth. Why would this be unconditionally inferior to sticking a rod in a ground, if at all? The Earth can store a charge. So can a positive electret. What I want to know is why a bunch of dirt on the ground will work, and yet you say a positive electret will not. In both cases, we are talking about something having a "higher" potential, so why will a positive electret not work? Let's assume that in both cases, we have significant surface area for which the charge to be drawn into (e.g. a long grounding rod and an electret with plenty of internal area).
     
    Last edited: Jul 23, 2012
  17. Jul 23, 2012 #16

    Dale

    Staff: Mentor

    Yes. That is what you do when designing safety circuitry. You make an assumption about a possible failure mode and design a circuit that avoids harm in that failure mode. You repeat that process for as many possible failure modes as you can come up with.

    You are missing the whole point. What is harmful is current. The safety aspects of grounding have to do with providing an alternative path for current, not with charge storage.

    Charge (and voltage) is not particularly harmful, e.g. have you ever seen a picture of a person touching a Van de Graff generator with their hair sticking out. They are significantly charged, but unharmed because the current is low.

    Because a positively charged electret will draw current through a grounded human to the electret.

    Not only does the positively charged electret provide an EMF to drive current, it also has a high resistance. The ground is a low resistance path for current, the electret is made of dielectric materials, so it is high resistance. Current from other sources will preferentially go through the low-resistance human rather than the high resistance electret.
     
    Last edited: Jul 23, 2012
  18. Jul 23, 2012 #17
    Ok, now that I have my question answered. I have the following that I am still wondering about.

    What would it take to make a little box the size of, say a Big Mac container, while serving the same quality of electrical grounding as a grounding rod in that you could throw one into the air to absorb a lighting strike without further discharging the energy into the earth, even when the box lands on the ground?
     
  19. Jul 23, 2012 #18

    Dale

    Staff: Mentor

    I don't know enough about lightning. So, at a minimum it would take someone with a better understanding of lightning than me and some electrical engineering background.
     
  20. Jul 23, 2012 #19

    Drakkith

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    Staff: Mentor

    It is not possible. The amount of charges transported by a lightning strike is about 15 coulombs. An object the size of a big mac container would have to contain all this charge, which means it would need to be positively charged at about the same amount. Two charges of 7 colombs placed 0.1 meters apart would experience a force of 4 x 1015 newtons, or about the force that 40 billion metric tons of mass would place on the ground. The container is impossible to make. And if you could make it, it would explode instantly with nuclear weapon energy.
     
  21. Aug 14, 2012 #20
    A few weeks ago I had another thought.

    Although it's not possible to do this with a positively charged electret (in of itself), I figured that if the energy of the spark (in this case, lighting) were used to draw in positive ions from the atmosphere into the object at the same time that electrons would be drawn in from the lighting bolt, then it would be possible to absorb the lighting bolt in an small volume, in effect, creating an effective ad hoc electrical ground that could substitute for the earth (so as long the object to be protected would be "grounded" to this object). Of course, that is no longer characteristic of a positive electret, but it makes me wonder if it would in anyway be of great importance in miniaturizing grounding devices in general.
     
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