Van de Graaff Generator
A pulley drives an insulating belt by a sharply pointed metal comb which has been given a positive charge by a power supply. Electrons are removed from the belt, leaving it positively charged. A similar comb at the top allows the net positive charge to spread to the dome.
Principle Of Van De Graaff Generator
Two main principles of Van De Graff Generator are given below:
*It is designed on the basis of the property that the charge given to a conductor which is hollow inside, is transferred to the outer surface and scatters uniformly over it.
*It is founded on the phenomenon of Corona Discharge.
There is a large spherical conductor named S having a few meters of radius. It is placed on two pillars at a certain height from the ground. One is P1 and other is P2. A belt made up of insulating material is moving over two pulleys P1 and P2. The pulley P2 is present at the center of the spherical conductor S and the pulley P1 is present near the ground. A motor is used whose main function is to create a spin in the belt. Two sharp headed combs, B1 and B2 are used. Spray Comb and collecting comb are the names of B1 and B2 respectively. A discharge tube D is used in which the acceleration of ions is done. The point from where the ions originate is present at the head end of the discharge tube. But the other end of the tube is earthed.The whole apparatus is placed in a steel compartment .Compartment is filled with Nitrogen or Methane. The preassure inside the chamber is maintained very high.Working Of Van De Graaff Generator
A simple Van de Graaff generator consists of a belt of silk, or a similar flexible dielectric material, running over two pulleys, one of which is surrounded by a hollow metal sphere. Two electrodes in the form of comb-shaped rows of sharp metal points, are positioned respectively near to the bottom of the pulley and inside the sphere. One electrode is connected to the sphere, and a high DC potential (with respect to earth) is applied to the other electrode; a positive potential in this example.
The high voltage ionizes the air at the tip of second electrode, repelling (spraying) positive charges onto the belt, which then carries them up and inside the sphere. This positive charge induces a negative charge to the electrode and a positive charge to the sphere (to which electrode is connected). The high potential difference ionizes the air inside the sphere, and negative charges are repelled from brush and onto the belt, discharging it. As a result of the Faraday caqe effect, positive charge on electrode migrates to the sphere regardless of the sphere's existing voltage. As the belt continues to move, a constant charging current travels via the belt, and the sphere continues to accumulate positive charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current. The larger the sphere and the farther it is from ground, the higher will be its final potential.
The high voltage ionizes the air at the tip of second electrode, repelling (spraying) positive charges onto the belt, which then carries them up and inside the sphere. This positive charge induces a negative charge to the electrode and a positive charge to the sphere (to which electrode is connected). The high potential difference ionizes the air inside the sphere, and negative charges are repelled from brush and onto the belt, discharging it. As a result of the Faraday caqe effect, positive charge on electrode migrates to the sphere regardless of the sphere's existing voltage. As the belt continues to move, a constant charging current travels via the belt, and the sphere continues to accumulate positive charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current. The larger the sphere and the farther it is from ground, the higher will be its final potential.
