VAN DE GRAAFF

VAN DE GRAAFF GENERATOR:

PRINCIPLE: 

  *IT WORKS ON THE PRINCIPLE OF ELECTROSTATIC INDUCTION AND ACTION OF POINTS.

CONSTRUCTION:

 * 'A' BE THE HOLLOW METALLIC SPHERE MOUNTED ON INSULATING PILLARS.

 * 'B' AND 'C' BE THE TWO PULLEYS.'B' IS MOUNTED AT THE CENTRE OF THE SPHERE AND 'C' IS MOUNTED NEAR THE BOTTOM.


 * PULLEY 'C' IS DRIVEN BY AN ELECTRIC MOTOR.


 *A SILK BELT MOVES OVER THE PULLEYS.

 *'D' AND 'E' BE THE TWO COMB SHAPED CONDUCTORS HAVING SHARP NEEDLES WHICH ARE MOUNTED NEAR THE PULLEYS.


 *COMB 'D' IS GIVEN A POSITIVE POTENTIAL (10^4 V) BY A POWER SUPPLY.


 *COMB 'E' IS CONNECTED TO THE INNER SIDE OF THE HOLLOW SPHERE.

WORKING:

 *SINCE HIGH ELECTRIC FIELD IS AT 'D' AIR GETS IONISED DUE TO ACTION OF POINTS.

 *NOW THE NEEDLE ATTRACTS NEGATIVE CHARGES AND REPELS POSITIVE CHARGES TOWARDS THE BELT.

 *THE POSITIVE CHARGES STICK TO THE BELT, MOVES UP AND REACHES 'E'.


 *'E' ACQUIRES NEGATIVE CHARGES DUE TO ELECTROSTATIC INDUCTION AND SPHERE ACQUIRES POSITIVE CHARGES  WHICH ARE DISTRIBUTED ON ITS OUTER SURFACE.

  *THE HIGH ELECTRIC FIELD AT 'E' IONISES THE AIR AND HENCE NEGATIVE CHARGES ARE REPELLED TOWARDS THE BELT.


 *DUE TO THIS THE POSITIVE CHARGES ARE NEUTRALISED BEFORE THE BELT MOVES OVER THE PULLEY.

 *SO THE DESCENDING BELT IS LEFT UNCHARGED.


 *THE POTENTIAL OF THE  SPHERE KEEPS ON INCREASING AND REACHES A MAXIMUM OR LIMITING VALUE.


 *AFTER THIS STAGE LEAKEGE OF CHARGES OCCUR DUE TO IONISATION OF AIR.

ROBERT J.VAN DE GRAAFF

 *THIS LEAKAGE CAN BE REDUCED BY ENCLOSING  THE MACHINE IN A GAS FILLED STEEL CHAMBER AT A VERY HIGH PRESSURE.

USES:

 *USED TO PRODUCE LARGE ELECTROSTATIC POTENTIAL DIFFERENCE UP TO 10^7  V.

 *THIS HIGH VOLTAGE IS USED TO ACCELERATE THE POSITIVE IONS (PROTONS,DEUTRONS ) FOR NUCLEAR FISSION PROCESS.