Van de graaff Generator Principle | Construction | Working

Van de Graaff Generator is a device for producing a larger electrostatic potential difference of an order of 10^7 (V). The Van de Graaff Generator was invented by a Robert. J. Van de Graaff in 1929, so the device got the name Van de Graaff Generator.

Principle:

The basic principle behind the working of Van de Graaff generator was Electrostatic Induction and Action of points. 

Construction:

• The top part of the Van de Graaff generator consists of a hollow metallic sphere which is mounted using the insulating pillars. The hollow metallic sphere is denoted by A.
• The top part of the Van de Graaff generator ( the metallic sphere) consists of a pulley B and the bottom part of the Van de Graaff generator consists of a pulley C.
• The middle part consists of insulating pillars, inside which the belt passes through the pulley.
• The belt is made up of a silky material which moves continuously over the pulley.
• The belt is made to rotate with the help of an electric motor which is connected to the pulley.
• Two combs (conducting materials) E and D which consists of needles are placed at the top and the bottom respectively.
• The Comb D is provided with an electric potential 10^4 V.
• The Comb E is placed inside the hollow metallic sphere.

Working:

• The High electric field near the Comb D, makes the air to ionize due to the action of points.
• The positive charges are repelled on towards the belt and the negative charges are attracted towards the Comb D.
• The repelled positive charges which are stick to the belt is taken up to the Comb E.
• Then the electrostatic Induction makes the Comb E to acquire a negative charge and the sphere acquires a positive charge.
• The outer side of the sphere consists of positive charges. (Acquired positive charges)
• The ionization of air takes place at the Comb E and the negative charges are neutralized by the acquired positive charges.
• The neutralization of charges takes place at the pulley (B) region and the belt moving towards the Pulley (C) won’t have any charges.
• The process will repeat ‘n’ number of cycles and at one stage, there won’t be any spaces for positive charges and the leakage of charges will occur on the machine.
• The limiting point is a term used to denote the peak point before starts to leakage.
• By using the gas-filled steel chamber at high pressure, the leakage of charges due to an air ionization can be reduced.

Advantages: 

• We are giving the input in the order of 10^4 volt but we are getting 10^7 volt.

Disadvantages: 

• Leakage of charges at the final stage of each and every cycle.

Applications: 

•  The high voltage produced from this Van de Graaff Generator can be used to accelerate protons and deuterons for the purpose of nuclear disintegration.