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Van de Graaff Generator Class 12 Physics Electrostatic Potential And Capacitance

Van de Graaff Generator

    It is an arrangement established by Van De Graaff to building up high potential difference of order 10^7 volts. It works on the following two principles
  1. The charges given to the sphere spread to the outer surface of the conductor             
    if two concentric spherical conductors are connected by a wire, the charges will flow from the inner conductor to outer conductor, whatever be the potential of the conductor.

 
  2. Discharging action of sharp points ( Corona Discharge )
    
    The surface charge density of a conductor is σ=Q/A.  which means the charge density is more in small or sharp region. 

Construction Of Van de Graaff Generator

It consisted of a large hollow metallic sphere mounted on two insulated supporting columns. An endless belt of an  insulating material (Nylon) is mounted on pulleys P1 & P2 which is run by a motor. Two sharp metal combs C1 and C2 are fixed near the pulleys P1 and P2 respectively. Comb C1 is connected to a high voltage battery.

Working Of Van de Graaff Generator

Hence the high voltage (positive terminal ) is connected to comb C1, C1 contains positive charges. As we know the charge densities are high at the pointed region. so the positive charges accumulate in the pointed region of the metal comb. 


When the belt comes in contact with the comb C1, the positive charges pass to the belt.
As the belt moves to the top ( because it is connected with the motor) it carries the positive charges along with it.

When the belt reaches the top of the pulley P2. it transfers the positive charges to another comb C2


As we discussed earlier the charges given to the sphere will spread to the outer surface of the conductor. ie the comb C2 pass transfer all the charges to the sphere. 

The belt comes back and this process continues  
                                              

Uses Of Van de Graaff Generator

  • it is used to create high potential 
  • it is used to accelerate protons, atoms etc
  • used to study collision experiment'
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