Question

Explain the principle, construction and working of Van de Graff generator.

Answer 1

Hint: Van de Graff generator uses principles of electrostatics generator; it uses a moving belt that accumulates charge on a hollow metal structure. The structure of the Van de Graff generator consists of terminals, brushes, pulley, spray comb, motor and a narrow conveyor belt. This generator is used for building high potential differences.

Complete step by step answer:
Van de Graff generator is an electrostatic generator which is used for building up extremely high potential differences. This potential difference is up to millions of volts though it normally produces potential difference in the order of mega volts.
Construction:

The Van de Graff generator consists of a rubber belt running over a pair of rollers.
Construction: The upper end of the roller is connected to a hollow metallic sphere mounted over an insulated stand. The lower comb is connected to a power supply and the upper comb is connected to a hollow sphere. The lower roller is connected to the motor.
Principle of Van de Graff generator: Van de Graff generator works on two principles;
I. Corona discharge: Corona discharge is caused by ionization of fluid around the conductor. In this case, the air is ionized.
Ii. Accumulation of charge on the outer sphere: All the charges supplied to the shell are uniformly distributed over its surface.
Working of Van de Graff generator: When the power supply is turned on, the lower comb starts to emit positive charge. This positive charge passes over to the belt and it is collected by the upper receiver comb which is connected to the metallic shell. The charges over the shell are uniformly distributed. As the belt continuously carries positive charge to the receiver comb, more and more positive charge gets accumulated over the sphere. This increases the potential on the sphere to a greater extent. It becomes difficult for the sphere to store this extra charge due to the force of repulsion between the light charges on the dome. When the potential of the shell exceeds the breakdown value of air. Air around the sphere gets ionized and leakage of charge takes place. As a result, the generator produces high-energy particles in the energy range greater than mega volts.

Note:
Depending on the material of the metallic shell it is possible to have a potential difference in the range of mega volts.
Power supply supplies positive charge to the hollow sphere which is uniformly distributed over the surface.
The increasing density of charge leads to discharge of charge.