Topic covered: Static ElectricitySI unit: Coulombs (C)
The electric charge of an atom depends on the valence electrons. When electrons are removed, the atom becomes positively charged and when electrons are added, the atom becomes negatively charged.
How the Van de Graaf generator operates:
The motor spins the non-conductive belt and this causes the air around the belt to move along with it, picking up charges from the electrical "hair". At the top of the belt, a metal plate that has metal teeth mounted on the surface facing the belt picks up the charges from the moving air caused by the belt. The charges flow along the conductive wire and onto the sphere, where the charges then spread out along its surface.
Explanations of the demonstrations done using the Van de Graaf generator :
1. When the hair comes into contact with the sphere, due to the difference in charge, the hair repels from the sphere causing it to stand upright.
2. The neutral styrofoam ball is attracted to the charged metal sphere.It gains electrons from the metal sphere when it comes into contact and becomes charged.This creates a difference in charge, causing the styrofoam ball to repel the sphere.