What is Van De Graaff Generator?
A Van de Graaff Generator is a device used for building up extremely high Potential Differences in the order of a few million (as high as 20 million volts). Currently, Van de Graaff Generator produces a Potential Difference of 5 Mega volts.
The Van de Graaff Generator was designed by Robert Jemison Van de Graaff in1929 A.D.
While standing on an insulated platform, if we touch the spherical part of this Generator, the charge of the sphere would pass along our body and would transmit to our hairs.
Since the same charge would produce on our hairs, and these charges would repel each other. This is what we could see in the picture below:
Van de Graaff Generators are delineated as the "constant current" electrostatic devices. When we put a load on a Van de Graaff Generator, the current remains constant., but the voltage alters with the load.
Introduction:
Van de Graaff Generator is one of the devices that has an insulating effect and helps insulate various objects by creating a very high Potential. There is the acceleration of particles that are observed. There is also the presence of atom smashers where the subatomic particles are exposed to high-speed acceleration and are then smashed into the target atoms. Due to this smash collision happening there is the production of other subatomic particles along with other high energy radiation being produced. In order to understand the use of the Van de Graaf Generator and its uses here is an article on Van De Graaff Generator - Introduction, Working, Principle, Construction and Uses via Vedantu that helps you get an idea about everything involved with the same.
Triboelectric Effect Seen in Van De Graaff Generator:
The triboelectric effect is a type of electrification in which certain materials tend to become charged electrically when they come into contact with one another and are then separated from each other. The polarity and strength of the charges that are being produced may differ in magnitude based on the materials that are used, surface roughness, temperature, strain, and other properties. To know more about the triboelectric effect students can also access the Vedantu NCERT Solutions for Class 12 Physics which provides a detailed view on the same.
On this page, we will learn about the following:
What is Van De Graaff Generator?
Working, principle, and construction of Van De Graaff Generator
Uses of Van De Graaff Generator
Principle
Van de Graaff Generators are “Constant Current” Electrostatic devices that work mainly on the two principles:
Corona discharge.
Accumulation of charge on the outer sphere.
Construction
(Image will be Uploaded Soon)
(Image will be Uploaded Soon)
Van De Graaff Generator Consists of the Following:
An outer terminal - An aluminum or steel sphere
Upper brush - A piece of fine metal wire
Upper pulley (P1) - A piece of nylon
A long narrow conveyor belt of insulating material like Silk, rayon or rubber wound around the pulleys P1 and P2
Motor
Lower brush
Lower pulley (P2) - A piece of nylon covered with silicon tape.
B1 - Sharply pointed spray comb
B2 - Sharply pointed collecting comb
Working
When the spray comb is given a positive Potential (= 104 volts) w.r.t. the earth via the high tension source H.T. Due to corona discharge action of sharp points, a positively charged electric wind is set up, which sprays a positive charge on the belt as soon the motor is turned on, the lower pulley (P2) begins turning the positively charged belt upwards, and the lower pulley (P1) establishes a negative charge. Since the pulley P2 is capturing electrons from the belt which is passing over this pulley P2.
Here, we can see that the charge on the pulley P2 is more concentrated than the belt because a strong electric field is generated at the lower pulley.
As the belt reaches the sphere, a negative charge builds upon the collecting comb B2 and a positive charge on the farther side of the comb B2.
This positive charge shifts to the outer surface of S. The discharging action of sharp points of the comb B2, a negatively charged electric wind is set up. Which in turn would neutralize the coated positive charge on the belt, and the belt would turn down again.
The belt will collect the positive charge from comb B1, and then would be collected by the comb B2.
This process continues, the charge accumulates on the sphere S and the excess charge shows up on the outer surface of the sphere.
Capacitance of electrical sphere
C = \[ 4 \times π \times 𝔪o \times R \] (R =radius of the shell)
C = \[ \frac {Q}{V} = \frac {V}{4 \times π \times 𝔪o \times R } \]
Where V is the Potential Difference
C = Capacitance
Q= The charge in the spherical shell
𝔪o =Permittivity of free space
Hence, the Potential Difference V increases with an increase in charge Q.
As soon as the Potential of the shell exceeds the breakdown field value of air (\[3 \times 10^{6}\] Volt /meter), the air around S gets ionized, and leakage occurs.
This leakage is minimized by housing the shell inside the steel chamber filled with nitrogen and methane at high-pressures.
Uses of Van de Graaff Generator
Particle Accelerators
These accelerators are also known as Particle Smashers. The high energy supply by the Generator accelerates the subatomic particles in an evacuation tube, and these particles crash into atoms.
The ability of a Generator to create these high-energy collisions is the cornerstone of Particles and used to accelerate ions, protons, and electrons needed for various experiments of Nuclear physics.
These Generators are used as accelerators to generate X-Ray beams for nuclear research and nuclear medicine.
Science Education
In physics education to teach Electrostatics.
Sterilizing Food
Accelerates electrons to sterilize food and process materials
Summary
There are two kinds of Van de Graaff Generators: The one employs high-voltage power supply for charging and one utilizes belts and rollers for charging.
Van de Graaff Generator, as we set about the output terminal (sphere) with a grounded object, the voltage will decrease, but the current will remain the same.
The charges are produced due to friction by two insulating bodies rubbing against each other, and they can’t move on their own (at rest) which means they (charges) are static by nature are called Static charges.
FAQs on Van De Graaff Generator
1. How can you Prevent Corona Discharge?
Corona discharge depends upon various factors:
Shape: A smooth surface (electric field uniformly spreads) would have less corona than the stranded surface (as electric field distributes over the surface at different locations).
Size: Conductors having a large diameter have fewer chances of corona discharge.
Line Voltage: Lesser the line voltage, less will be the corona discharge.
2. How can the whole Charge of a Conductor be Transferred to another Isolated Conductor?
This can be done by placing a hollow insulated conductor inside the charged conductor and connecting the two conductors by a wire, the whole charge will shift to the isolated conductor.
3. A Spherical Shell of Radius k with Charge D is Spread out to Radius h. Find the Work done by the Electrical Force in this Procedure.
Work done = Initial Stored energy - final stored energy
Since the formula is given by W=\[ \frac {1}{2} \times D^{2} \frac {𝔪}{r}\]
=\[\frac {1}{2} \times D^{2} \frac {4}{π} \times {𝔪} \times {k}- \frac {1}{2} \times D^{2} \frac {4}{𝔪} \times {π} \times {h}\]
Therefore, Work done = \[ D ^{2} \frac {8}{π} \times {𝔪}\]
1/k−1/h
4. Two Insulated Spheres of Radii 40 cm and 56 cm Holding a Similar Charge are Wired by a Conductor and then they are Set Apart. Which of the Two Spheres will Carry More Charge?
Bigger sphere will carry more charge as its capacity is larger (D = M x G). The Potential Difference G turns the same on getting them attached with a wire.
5. What are the components of the Van De Graaff Generator?
The components of the Van De Graaff Generator can be provided as follows:
1. Hollow metal sphere supported by insulating supports through its sides
2. Upper electrode
3. Upper gaseous roller (for example it can be an acrylic glass)
4. Side of the belt with the presence of positive charges
5. The opposite side of the belt with negative charges being present
6. Lower metal roller
7. The lower ground electrode
8. An aspherical device with negative charges present
9. The spark that is produced due to the presence of different Potentials
6. What is the use of learning about the Van De Graaff Generator - Introduction, Working, Principle, Construction and Uses via Vedantu?
By learning about the Van De Graaff Generator - Introduction, Working, Principle, Construction, and Uses via Vedantu students get to learn regarding the following:
1. Students can learn how to use the Van De Graaff Generator for creating a Potential that ranges around a few million volts
2. How the protons, deuterons, etc can be accelerated and hence bring about artificial transmutation
3. It will help to learn more about collision experiments that are present in Physics
4. How the beams involved can be used to treat cancer.
7. Where is the Van De Graaff Generator used?
In recent times the Van De Graaff Generator is largely used to demonstrate various aspects and concepts involved in the electrostatic behavior of particles in academic sessions. However, in the earlier times, it was mainly one of the sources that were used to accelerate various subatomic particles. Now due to the advancements in science, it has become possible to use much better instruments than Van De Graaff Generator. Even if the use of the Van De Graaff Generator is very restricted to only demonstration purposes, it once used to have a good history as a part of nuclear physics.
8. What are the limitations of the Van De Graaff Generator?
There are certain limitations with its usage and these limitations can be provided as follows:
1. It has a series combination that allows only one route for the motion of the charges that are involved, hence making it impossible for the scattering of particles.
2. It can only be used to accelerate the charged particles and not the uncharged particles. Hence it has only a limited range of applications.
Due to these two limitations, it is not feasible to use the Van De Graaff Generator for measurement purposes. The charge being involved is also quite dangerous and hence is only allowed for demonstration purposes.
9. What are the precautions and safety measures needed to be taken while accessing the Van De Graaff Generator?
Van De Graaff Generator is an instrument that dissipates a high amount of charge hence there needs to be some precautions and safety measures that needs to be followed:
1. Those people who have cardiac pacemakers attached should not be close to the Van De Graaff Generator or even come in contact with it
2. While the Van De Graaff Generator is being charged make sure that you stay at least three feet away.
3. Always make sure that you discharge the collector dome between two experiments when you are done with the demonstration. You can use the discharge wand for this purpose.
4. The voltage is so high that it can make its way to your body through the discharge wand and hence make sure you hold it only by the handle and do not touch anywhere else.
5. Do not run the Van De Graaff Generator for a longer period of time continuously
6. Make sure you have kept the entire device dry and clean