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Some basic questions

  1. Aug 15, 2003 #1
    I am in a spot of bother. Actually I live in an under developed country where science and technology is not upto the modern standards and there is very little practical facilities. I wanna ask if I have a metal sheet of some thickness how it could be made permenantly positive and permenantly negative and is it possible that a plate is positively charge for one second and it is negatively charged in the other by any means. And lastly if one plate is positive and other is negative will they actually move toward each other and positive-positive will move away from each other.
  2. jcsd
  3. Aug 16, 2003 #2
    No, you can't permanently have a positive charge on one side and negative on the other. Metals try to keep electric fields from penetrating them so the field inside is zero. This property means that if you have a uniform electric field perpendicular to your metal plate it will have a positive charge on one surface and a negative charge on the other. But when you take the field away the charges move around to cancel again. So all you need is a permanent electric field.

    If the plate is connected to an alternating source of potential then the charge on the plate will oscilate. You have essentially built a capacitor with the plate and ground.

    If one plate is positive and one is negatively charged then they will try to move toward each other. If they are free to move then they will move. It's possible to calculate the force on each plate if you know the charge density, the separation and the area.
  4. Aug 18, 2003 #3
    if you're interested in electrostatic experiments, I think it's not a big drawback if you have only simple equipment at hand. On the contrary, since most of the effects have been discovered in ancient times, it should be possible reproducing them with simple equipment today.

    First, you need a simple device which reliably indicates electric charge. Two thin strips of aluminum (e.g. from a chocolate wrapper) will do. Hang them down from a piece of uninsulated wire, and stick the wire thru a small bottle's cork from its bottom. Then replace the cork into the bottle, so that the strips hang freely inside. You might want to attach a small metal ball (crumpled aluminum) to the top end of the wire sticking out of the cork. Now you have an electroscope.

    Next, try rubbing agents. A plastic ballpen might do. Rub it fast, but not hard, against some fur (I use my own hair), and then try to transfer the electricity to your electoscope. If there is any charge, the aluminum strips will spread apart and stay like this. You can discharge them by touching the conductor ball with your finger.

    Play around with different rubbing agents, modify your electroscope, and so on. I'm sure you will discover all major effects in static electricity, and... it's fun!
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