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Can an electrostatic force repel or just attract?

  1. Mar 8, 2008 #1
    [SOLVED] Can an electrostatic force repel or just attract?

    Two charged plates can't be made to repel each other right?
  2. jcsd
  3. Mar 8, 2008 #2
    Yes they can, just not on the same potential ofcourse

  4. Mar 8, 2008 #3
    So, a positively charged plate will be attracted to a grounded plate and a negatively charged plate will be repelled by a grounded plate.

    Sorry if i make no sense, i have myself confused.

    Edit: This makes no sense because as long as there is potential difference between the plates they will attract each other. What scenario would cause repulsion?
    Last edited: Mar 8, 2008
  5. Mar 8, 2008 #4
    No. A ground plate is inherently at 0V. It is connected to earth which by definition in electronic engineering (and perhaps physics) a source of infinite charge, both positive and negative.

    A negatively charged plate will induce a positive charge on an earthed plate and they will attract. A positively charged plate will induce a negative charge on the earthed plate and also attract. It is only if you get like with like....so two positively charged or two negatively charged.
    Last edited: Mar 8, 2008
  6. Mar 8, 2008 #5
    How would i make two plates repel each other then? I tried hooking the positive of a 15kv hene ballast to two plates and nothing happened. This would work if i had two separate supply's correct?
  7. Mar 8, 2008 #6


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    Staff: Mentor

    It's probably because the force that the places exert on each other is too small to be easily observed or measured. Have you tried to calculate it?
  8. Mar 8, 2008 #7
    Yes. Since like charges repel and unlike charges attract all you have to do is simply place charge of one sign on one plage and charge of the opposite on the other plate.

    Best wishes

  9. Mar 9, 2008 #8
    The plates snap together with 15kv between them, i would think should be able to repel each other with the same force? I have tried calculating it but i don't know if what i am calculating is correct.

    Yes, i have done that and it worked very well. But how do you make them repel each other.
    Last edited: Mar 9, 2008
  10. Mar 9, 2008 #9
    Perhaps there is some flaw in your experimentation? I am not familiar with a 15kV hene ballast. When you perform the experiment with the plate charges equal and opposite to one another how do you connect the equipment?

    How do you connect it in the experiment to charge the plates with like charges?
  11. Mar 9, 2008 #10
    To make them attract i simply hook the positive to one plate and the negative to the other. In an effort to try to make them repel i hooked the positive to both plates while grounding the negative, and nothing happened.
  12. Mar 9, 2008 #11


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    Staff Emeritus
    Science Advisor
    Education Advisor

    You seem to have a lot of confusion here. Go back to something simpler. Have you ever played with an electroscope before? Try to figure out the nature of the charge induced in there.

  13. Mar 10, 2008 #12
    hi ak_47_boy i am ricardo19 an aswer to your question

    different polarities atract and equal polarities repel
    follow this example am sending you, and tell me if it was good for you
  14. Mar 10, 2008 #13
    http://www.gcsescience.com/Attract-Repel-Electrostatic-Charges.gif [Broken]
    Last edited by a moderator: May 3, 2017
  15. Mar 10, 2008 #14
    The reason that the plates with opposite charges attract so much more than like charged plates repel, if you put the same voltage on them Is that there is much more charge on them. Because the opposite charges attract each other more charge is drawn into the plates. If you put the same charge on the plates this will oppose the buildup of charge.

    If you want to compare repulsion and attraction there are two ways:

    1 charge the opposite charged plates when they are far away from each other, then disconnect the voltage source and bring them together. you should see the same
    repelling force as you previously did.

    2 use two sets of plates that you give opposite charges. Disconnect the voltage source and then bring two plates with the same charge together.

    If you pull apart a charged capacitor, the voltage will go up.this could lead to leakage, sparks AND BE DANGEROUS IF YOUR CAPACITOR WAS BIGGER THAN 1nF.
    I have seen this experiment done. you need to cover the edges of the plates with a good insulator and put some grips on them made of an isolator. Do not put the plates near anything that isn't a good insulator (such as yourself)
    If you use 100 cm^2 plates with 1 cm initial distance there isn't any danger, but your charge might easily leak away if you're not careful.
  16. Mar 10, 2008 #15
    Ok, I have it working just as you described.

  17. Nov 5, 2009 #16
    Re: [SOLVED] Can an electrostatic force repel or just attract?

    I have this project on moon colonisation. when i was researching i came across moon dust aka regolith. this substance has a net positive charge. i thought that some how negatively charging a space suit would solve this problem. is this possible? any other ideas?

    Also is it possible to crate a "wall" of electrons or negative electroststic charge, like a shield, around a person?
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