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6 mark phy6 question, can you get all marks? watch

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    (Original post by Migraine)
    I thought a van de graaff worked as follows:

    The belt on the van de graaff acumalates a positive charge by friction, which then repels other positive charges upwards onto the top sphere (Although i guess what its really doing is attracting negatives from the top sphere leaving an excess of positive?). When the Potential difference accross the top sphere and the (earth?) becomes great enough (I think its in the region of MeV?) This ionises the air molecules around the top sphere.

    In the case of the van de graaff in schools i think the positive charge on the sphere attracts electrons from the earth up the second sphere, and when enough air has been ionised, a charge can flow from the negative second sphere through the air to the first positive sphere, causing a spark to show.

    I dont see how this fits in with accelerating particles though, unless you simply place a positive particle (such as an alpha particle) near the positive dome and it gets repelled away?
    i thought positive charge can't move, only the negative charge can be moved :confused:

    Which is why i wrote in brackets that the postivie charge attracted electrons from the top sphere, leaving an excess of positive charge
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Updated: June 26, 2005
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