Physics > Capacitors > 15.0 Van De Graaff Generator
Capacitors
1.0 Introduction
2.0 Different types of capacitors and its capacitance.
3.0 Parallel Plate Capacitor
3.1 When equal and opposite charges placed on plates
3.2 When unequal charges are placed on the two plates
4.0 Capacitance of spherical conductor
5.0 Capacitance of a earthed sphere by a concentric spherical shell
6.0 Capacitance of a cylindrical capacitor
7.0 Mechanical force on the charged conductor
8.0 Redistribution of Charge
9.0 Dielectrics (Insulators) and Polarization
9.1 Effect of Dielectric
9.2 Capacitance of a Capacitor Partially Filled with Dielectric
9.3 Quantities after inserting dielectric in a capacitor (fully)
10.0 Combination of capacitors
11.0 Energy Density ($u$)
12.0 $R$-$C$ Circuits
13.0 Method of Finding Equivalent Capacitance
14.0 Some important concepts
15.0 Van De Graaff Generator
15.2 Construction
3.2 When unequal charges are placed on the two plates
9.2 Capacitance of a Capacitor Partially Filled with Dielectric
9.3 Quantities after inserting dielectric in a capacitor (fully)
A large spherical conducting shell (of few meters radius) is supported at a height several meters above the ground on an insulating column. A long narrow endless belt insulating material, like rubber or silk, is wound around two pulleys – one at ground level, one at the center of the shell.
This belt is kept continuously moving by a motor driving the lower pulley. It continuously carries positive charge, sprayed on to it by a brush at ground level, to the top. There it transfers its positive charge to another conducting brush connected to the large shell.
Thus positive charge is transferred to the shell, where it spreads out uniformly on the outer surface. In this way, voltage differences of as much as $6$ or $8$ million volts (with respect to ground) can be built up.
