· Most people will be familiar with the Van de Graff generators and hair standing on end. Here is a more accurate explanation of why. The force one point Q1 exerts on another point charge q2 distance r away is:
· F = kQ1q2
· K = 1/(4pe0) where e0 is the permittivity of free space so
ü F = 1 Q1q2
· Around electrical charges we can imagine an electric field, a region in which an electric charge experiences a force.
ü F = QE
· The direction of the field naturally depends on the charge, the arrows are drawn to represent the direction of the force on a small positive charge +q, so the field lines for a point positive charge go radially outwards, those for a negative charge radially inwards. Hence a repulsive force between two like-charged particles is taken to be positive.
· As E=F/q, E=( kq1q2/r2)/q;
ü E = 1 Q
· Energy = F x d so, similar to gravitation, potential energy Ep is given by
ü Ep = 1 Q1q2
· Electrical potential is the potential energy per unit charge (V=energy/q), so V=(kq1q2/r)/q;
ü V = 1 Q
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