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Van der graaf generator and tesla coil

  1. May 28, 2008 #1
    Hello peoples.
    Im attempting to build a van der graaf generator and a small tesla coil. Hopefully I have come to the right place for help.
    Firstly I'll start with van der graaf generator. I am going to use pvc lower roller (negative charge) and nylon upper roller (positive). any suggestions on better materials for rollers for better results.? also i was wondering if a woven polyester strap as used for tie down straps on trucks etc will work as a belt?
    I am trying my hardest not to buy anything for generator build and would love to make it from found / scavanged items , re the strap question.
  2. jcsd
  3. Mar 2, 2009 #2
    Sorry if I underestimate your current knowledge. I'm going to explain things fairly simply.

    When looking for materials to make a van der graaf generator out of, there are two main things to consider:

    The first is "electron affinity".

    "Electron affinity" is a property of a material that is basically how much it "likes" electrons.
    Rubber has a higher electron affinity than your hair, so, when you rub a (neutrally charged) rubber balloon on your (neuterally charged) head, the balloon takes electrons from your hair. There is now a charge "separated" between the balloon and your head. The balloon has a negative charge and your hair has an equal positive charge. Rubbing two materials together to separate a charge is called the "triboelectric effect". The greater the difference in electron affinities of two materials, the easier it will be to separate a charge by rubbing them. If material A "really likes electrons" and another "kinda likes electrons", you will be able to separate a charge between them by rubbing them, but not as easily as you would with material A and a material that "frackin' hates electrons".

    A van der graaf generators work because of the "triboelectric effect".
    A triboelectric series is a list of materials in order of their electron affinities. So, the further apart materials are on the list, the easier it is to separate a charge by rubbing them, so the better they will be for a van der graaf generator.

    Here is a triboelectric series:


    See how far apart human hair and rubber are? That's why rubbing a balloon on your head is so effective at separating a charge.

    The second thing to consider is "conductivity" which is a property of a material that describes how easy it is for electrons to flow through it.

    A van der graff generator has three main parts: a ball for collecting charge, a ground to "harvest" the charge, and a belt to take the charge from the ground to the ball.
    If the belt is too good a conductor, the charge won't stay on the ball, it will just escape through the belt and into the ground.
    If the ball is to poor a conductor, the charge won't arc to your finger, which is what I assume you are doing this for :)

    Anyway, good luck with your building!
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