011-40705070  or  
Call me
Download our Mobile App
Select Board & Class
  • Select Board
  • Select Class
Madumeethasri Vasudevan from OUR OWN ENGLISH HIGH SCHOOL , asked a question
Subject: Physics , asked on 21/9/12

give the principle construction and working of vande graph generator with neat diagram?


Jyoti Pant ,Meritnation Expert added an answer
Answered on 21/9/12

Vande graff generator:

In a Van de Graff generator a hollow metallic sphere is mounted on an insulating stand. The pulley at the center of the sphere is connected to the pulley at the bottom of the machine by an insulating belt of silk. 

This pulley is continuously driven by a motor. Two comb shaped conductors are mounted near the pulleys. Both the combs touch the belt. The lower comb is maintained at a positive higher potential of the order of 10 4 volts by a power supply. The upper comb is connected to the metallic sphere. 

The high electric field near the lower comb ionizes the air and makes it conducting. The negative charges in the air move towards the comb and positive charges stick to the belt. As the belt moves the positive charge is carried upwards. The charge on the belt near the upper comb again ionizes the air. Thus the positive charge on the belt is now transferred to the metallic sphere. (This is the working of the metallic comb) 

The machine continuously transfers positive charge from the power supply to the metallic sphere. The potential of the sphere keeps on increasing. If the electric field just outside the sphere is 3 Х 10 6 Volt per meter, dielectric break down of air takes place. 

The main limiting factor of this high potential is the radius of the sphere. The potential can be increased further by enclosing the sphere in a highly evacuated chamber.

This conversation is already closed by Expert

View More