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Electric force in electric field

  1. Dec 17, 2008 #1
    I have a question about whether a conductive wire is under any electric force if placed in a electric field. The setup is as following.

    A metallic needle is placed above a grounded metal plate at a distance of 100mm. the diameter of the needle is about 1mm, the length is about 20mm. The needle is pointing at the grounded plate. A 10kv supply is connected to the needle. So a electric field is created.

    now on the grounded metal plate, there is a very thin wire about 30mm long, with one end attached to the grounded metal plate. the other end of the wire is at loose. My question is whether the thin wire feels an electric force and aligns along the electric field? (assume the wire is very easy to bend and nearly no mass)
  2. jcsd
  3. Dec 17, 2008 #2
    I suppose that the 10 kv supply will unleash its energy instantaneously. You must have a continous electric field to exert a power. I don't think that would work, other that warming up the needle. You may need to create a magnetic field.
  4. Dec 18, 2008 #3
    Thanks for your reply. But the high voltage supply will continuously apply 10kv to the needle. And there is no other connection to the needle. So no current will be generated in the needle.
  5. Dec 18, 2008 #4
    Charged particles, like electrons, are deflected in an electromagnetic field...so a force will be exerted on a current carrying conductor in a strong enough field....
  6. Dec 19, 2008 #5
    If the needle had a positive charge with respect to the wire (ie the pos side of the 10kV connected to the needle and the neg side to wire or plate) you would then create an electric field between the wire and the needle. If this is the case you are talking about there is an attractive force between the needle and the wire. This is described by Coulombs law. Under these conditions because the needle is so small the E flux at the tip of the needle would be pretty dense and could cause the air gap to become ionized and allow current to flow across the gap into the wire. I guess it would be similar to what happens when you hair is attracted to a balloon after you give it a negative charge by rubbing it on carpet. Hope this helps.
  7. Dec 19, 2008 #6


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    Homework Helper

    Absolutely, there can be electric force on the wire. I believe the concept you need is induced polarization.

    Here you may have some "problems" sustaining that voltage. I recommend either decreasing the voltage or increasing the height of the needle above the plate. I believe the concept you need is electrical breakdown (in air).

    Yes, assuming that you don't have the discharge problems that I alluded to above.

    This is simply not true.

    ... unless you have the discharge problem ...

    ... or a negative charge ...
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