answersLogoWhite

0


Best Answer

A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe. The potential differences achieved in modern Van de Graaff generators can reach 5 megavolts. Applications for these high voltage generators include driving x-ray tube, accelerating electrons to sterilize food and process materials, and acelerating protons for nuclear physics experiments. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance.

A simple Van de Graaff generator consists of a belt of silk, or a similar flexible dielectric material, running over two pulleys, one of which is surrounded by a hollow metal sphere. Two electrodes in the form of comb-shaped rows of sharp metal points, are positioned respectively near to the bottom of the pulley and inside the sphere. One electrode is connected to the sphere, and a high DC potential (with respect to earth) is applied to the other electrode; a positive potential in this example.

The high voltage ionizes the air at the tip of second electrode, repelling (spraying) positive charges onto the belt, which then carries them up and inside the sphere. This positive charge induces a negative charge to the electrode and a positive charge to the sphere (to which electrode is connected). The high potential difference ionizes the air inside the sphere, and negative charges are repelled from brush and onto the belt, discharging it. As a result of the Faraday caqe effect, positive charge on electrode migrates to the sphere regardless of the sphere's existing voltage. As the belt continues to move, a constant charging currenttravels via the belt, and the sphere continues to accumulate positive charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current. The larger the sphere and the farther it is from ground, the higher will be its final potential.

The Basis of Charge Generation

When we "rub" stuff we can generate small voltages that promote the movement of charges, specifically electrons. By rubbing the right kind of materials, we can maximize the generation of this static electricity, which is called triboelectric effect. It's a form of what is called "contact electrification" where moving a material against another creates static electricity that causes some charges to move. Have you ever done this? Sure you have. If you've ever pulled some plastic wrap off the roll, you've participated in a contact electrification experiment. The plastic wrap wants to go all kinds of ways and stick to itself. Static electricity in action. And we've all had a "zap" grabbing a doorknob after crossing a rug on a dry day. In the van de Graaff, the little motor drives the belt up and over the top roller and back down to the bottom one in a continuous loop. At the top, a little metal "comb" up there attached to the sphere and held just above the belt deposits electrons on that belt. They're being stripped off the sphere (by triboelectric effect) and being carried down to the base of the apparatus. A positive charge develops on the sphere. As we run the machine longer, more charges shift and the potential on the sphere (the voltage on the sphere with reference to the base, where the electrons are being deposited) increases.

By connecting a small metal ball on a wand that is tied by a wire to the base of the generator, we can collect those electrons that we've been stripping off the big hollow sphere. Now the voltage is building up between the hollow sphere and the ball. Soon the charge differential between the two surfaces rises to the point where the voltage breaks down the air between the two surfaces. (The air can no longer insulate the two spheres.) The atoms and molecules of air between the two surfaces are ionized and they will now conduct electric current. The current follows the ionized path, and the ionized air will emit light. We've actually created lightning between the two surfaces. And thousands or tens of thousands or volts can be created to cause the air to ionize and allow the arc to occur. This shifts the charge balance toward a more neutral state, and the generator will have to run more to "rebuild" the charge.

The more the distance between the surfaces, the higher the voltage necessary to break down the air in the gap between them and cause the arc. Naturally. Some of the big machines create hundreds of thousands of volts with ease, and can actually generate a potential difference of several million volts under the right conditions.

Wikipedia has a nice article on the Van de Graaff generator, complete with pictures. Need a link? Hey, this is WikiAnswers. Of course we got one for ya.

User Avatar

Wiki User

โˆ™ 2010-03-27 13:13:59
This answer is:
๐Ÿ™
0
๐Ÿคจ
0
๐Ÿ˜ฎ
0
User Avatar

Add your answer:

Earn +20 pts
Q: How does a Van de Graaff generator work?
Write your answer...
Submit
Related questions

How was the van de graaff generator discovered?

robert j van de graaff


When was the van de graaff generator built?

Invented in 1929 by American physicist Rob. J. Van De Graaff


Who is Robert van de Graaff?

Robert van de graaff was the inventor of the van de graaff generator and was also a scientistAnsweran artist from the 70' he made really good progressive rock music, highly recommended


Who is better van de craft generator or cyclotron give reason?

I assume you mean the "van de Graaff generator". Better for what, exactly? From what I read, they serve different purposes. Specifically as a particle accelerator, the van de Graaff generator has been superseded by other designs.


How do you create shock static electricity?

Van de Graaff Generator


What did Robert Van de Graaff invent?

He invented the electric generator.


Can you do an experiment with a van de graaff generator?

You can light a fluorescent bulb


Van de graaff water?

Van de graaff Wine


What does the van de graaff generator used for?

it creates an electric field around it self


How does the Van De Graaff generator works?

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe on the top of the stand. Invented in 1929 by American physicist Robert J. Van de Graaff, the potential differences achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance. It uses the principle of friction between dissimilar materials to create a electrostatic charge, much like rubbing a balloon on your hair to generate static electricity.


What is a Van Der Graph?

A Van de Graaff generator generates an electrostatic charge (like static electricity).


Why does your hair stand up when you touch a Van de Graaff generator?

There a static charge going through the Van de Graaff generator, that travels up your body and through your hair causing the individual strands to repel each other and stand on end.


How does a Van De Graaff generator build up static charge?

A Van de Graaff generator operates by transferring electric charge from a moving belt to a terminal, usually, a hollow metal ball. It is an electrostatic generator, similar in principle to what happens when you rub your feet against a carpet and touch your cat!


When was Jan van de Graaff born?

Jan van de Graaff was born in 1944.


When was Freek van de Graaff born?

Freek van de Graaff was born in 1944.


How many amps does a van de graaf generator use?

"A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe. The potential differences achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance." This is quoted from en.wikipedia.org(http://en.wikipedia.org/wiki/Van_de_Graaff_generator)


What are facts about the Van de Graaff generator?

They are used to make peoples hair stand up on their head.


A large electrostatic generator is commonly called a?

Van de Graaff. its not spelled wrong its just french.


What does the Van De Graaff Generator produces?

It produces a very high voltage of the order of 107 V


How do make static electricity?

Static electricity can be generated by a thing called a Van De Graff generator.A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe on the top of the stand. Invented in 1929 by American physicist Robert J. Van de Graaff, the potential differences achieved in modern Van de Graaff generators can reach 5 megavolts (courtesy of wikipedia) See the Related Links Below for more details.


When was Robert Van de Graaff born?

Robert Van de Graaff was born on December 20, 1901.


Why doesnt the student receive a shock when she stands on a piece of insulating material places her hand on top of a Van de Graaff generator and then turns the generator on?

She is not shocked. She becomes part of the dome of the Van de Graaff, and charges flow onto her body. They do not jump to her body through a spark, so she is not shocked.


Which pop group was named after a device which builds up electric charge on a metal sphere?

Van de Graaff generator


When was Robert J. Van de Graaff born?

Robert J. Van de Graaff was born on December 20, 1901.


When did William T. Van de Graaff die?

William T. Van de Graaff died on 1977-04-26.