Question

Let's say you place a metal tray of foam pieces on top of a Van de Graaff generator. You turn it on and nothing happens right away but in a few seconds the foam pieces begin flying out of the pan. Why does this happen?
A. The Van de Graaff generator produces an anti-gravity current.
B. The foam pieces have a lower density than air once they're charged.
C. The foam pieces acquire the same charge as the round shell of the Van de Graaff generator.
D. The foam pieces build up an opposing electric field to the Van de Graaff generator and cancel its effect.

Answer 1

'A' is absurd.
'B' is false.
'D' is fanciful.

'C' is true.  When all the foam pieces have the same charge,
and enough of it, they repel each other with enough force to
fly apart from each other.