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Why does shuttling ball travel faster if plates are closer together?

  1. Jun 24, 2013 #1
    Shuttling ball.
    I was told that as the two conductive plates are brought closer together the speed the shuttling ball travels between them is increased. I don't understand this as i thought because the electric field is uniform between plates the distance they are apart wouldn't affect the attraction of the ball towards them. Could anyone explain this, thanks.
  2. jcsd
  3. Jun 24, 2013 #2

    Philip Wood

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    Gold Member

    The field IS uniform as we go across the gap from plate to plate and as we go across the gap parallel to the plates (except near the edge of the plates). But the STRENGTH of the field increases as the gap is diminished. This means that the ball's acceleration is greater. The ball has constant acceleration until it hits the opposite plate. But because the plates are closer together, it doesn't acquire any larger a final speed than when the plates were further apart. So its mean speed as it traverses the gap is the same whether the gap is smaller or larger, provided that the p.d. between the plates is the same.
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