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A Van de Graff generator is a machine that is used to generate electrostatic charges. This machine was invented by American physicist Robert J. Van de Graff. It works on the principle of electrostatics. In short, it is an electrostatic accelerator that is used chiefly in nuclear physics research experiments to get high voltages in less time with a high safety factor. The generated charges are used to increase the velocities of the subatomic particles, which may then find use in various fields.
The apparatus consists of two spheres that are maintained at different potentials. We know when there is a potential difference, charges flow, generating an electric current. We will learn in detail about the various principles such as corona discharge and the accumulation of charges on the outer sphere.
Van de Graff Generator
A Van de Graff generator is an electrostatic generator. This generator can be used to create a high potential in the range of a few million volts. It can be used to accelerate neutrons and protons. These accelerated particles can then strike a target and bring about artificial transmutation in the target element, which may result in the production of X-rays. Due to this application, physicists use a Van de Graff generator to study collision experiments. These fast-moving particles can be used in radiotherapy for cancer treatment.
Principles
We will now learn about the principle behind the working of a Van de Graff generator. To understand this, we need to understand certain basic terminologies.
What is corona discharge?
Corona discharge is defined as the phenomenon in which the electric discharge takes place in the air or gases of pointed conductors readily. Thus, corona discharge is one of the primary principles behind a Van de Graff generator.
If the charged conductor is brought in contact with a hollow conductor, then the charge (electrons or neutrons) transfers to the surface of the hollow conductor, and the charges that are accumulated then get spread uniformly all over the surface of the hollow sphere.
The above two points are the basic principles behind the working of a high-potential electrostatic generator.
To sum up the principles, they are :
Corona discharge (action at points)
Accumulation of charges on the outer sphere (electrostatic induction)
To explain in detail, the working of the generator is based on the following two principles;
Discharge action at sharp points (corona discharge), i.e., the discharge of charged particles takes place readily at pointed conductors.
If the charged conductor is brought in internal contact with a hollow conductor, the charge gets transferred to the hollow conductor and then spreads over the surface of this hollow conductor (in this case, the accumulation of charges on the outer sphere)
Components of a Van de Graff generator
From the principles we have learned, we can say that the basic requirements for a Van de Graff generator are:
A motor
Two roller systems
An insulated belt
Two brush assemblies and
A metal sphere
The motor is required to run the belt around the rollers. The belt must be moved at a constant velocity to achieve the desired result. When the motor starts running, the belt is moved, thus capturing electrons onto the insulated belt, and these electrons are then transferred to the roller. As sufficient charges are collected, there is the accumulation of charges on the roller. As the electrons are like charges, they repel each other. They also attract charged particles from the air between the roller and the brush assembly. Thus, positively-charged particles get carried on the belt. The belt is now positively charged and moves towards the upper roller. Now the electrons in the brush assembly become attracted to the positive charges on the belt. The sphere takes up all the positive charges, and the excess charge gets spread over the surface of the sphere.
This is the simple electrostatic working principle behind this generator.
Conclusion
In this article, we have learned about the principles as well as the working and uses of a Van de Graff generator. To summarise, a Van de Graff generator consists of a large spherical conducting shell. Using a moving belt and suitable brushes, the charge is continuously transferred to the shell, and a potential difference in the range of a few million volts can be generated. This high voltage can be used in various fields. One of the major applications of a high voltage is the acceleration of charged and uncharged subatomic particles such as neutrons and protons. These accelerated particles find use in various fields including radiation therapy treatment for cancer patients and collision studies in nuclear physics.
The two basic principles for this phenomenon are corona discharge and the accumulation of charges (through electrostatic induction). Using Van de Graff generators, a voltage difference of 6 to 8 million volts with respect to ground potential can be achieved.
