Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Experiment No. 4 Van de Graaff Generator Experiments Submitted by: Immanuelle Fyan C. Langoyan Student ID: 2022-1142 Date Submitted: May 25, 2023 Advanced Engineering Physics Laboratory ENS 140.1 Section 16B Instructor: Ryan G. Banal, D. Eng. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering I. Introduction In 1929, Robert J. Van de Graaff developed the first model of an electrostatic generator that consisted of a tin can, a motor, and a cheap silk ribbon. Named after him, the Van de Graaff generator is a physics classroom staple as it demonstrates the concept of building up static negative charges within a compact medium[1]. In this experiment, different procedures were performed that demonstrated various concepts of electrostatics using a Van de Graaff generator. The aim of this experiment was to educate and to provide a live, interactive, and safe environment for students in learning the field of electrostatics. II. Methodology/Procedure A. Materials and Setup of the Laboratory ▪ Van de Graaff generator ▪ Grounding sphere ▪ Head of plastic hair ▪ Neon indicator ▪ Aluminum helicopter propeller B. Procedure Part I. Making Sparks a. Touch the grounding sphere (connected to the ground wire to the dome. b. Turn the knob counterclockwise. c. Turn the generator on. d. Slowly turn the knob clockwise so the motor turns the belt. e. Take the small sphere away and let charge accumulate on the dome. (If possible, ask a student to turn off the lights to make it easier to see the sparks). f. Move the small sphere around the Van de Graaff sphere in different positions so that everyone in the room can see the sparks. g. Note down observations. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Part II. Head of Plastic Hair a. Turn the generator off and turn the knob counterclockwise. b. Ground the Van de Graaff sphere with the grounding sphere. c. Attach the head of plastic hair accessory. d. Turn on the generator and slowly turn the knob clockwise. e. Slowly approach the sphere with your hands without making contact. f. Note down observations. Part III. Human Hair a. Turn the generator off and turn the knob counterclockwise. b. Ask a participant to step up onto the insulated stool/plywood. c. Ground the dome using the grounding sphere. d. Without removing the grounding sphere, ask the volunteer to put one hand on the dome, the other hand by their side and make sure they understand not to move their hands until they are instructed to do so. e. Turn on the generator and turn the knob clockwise. f. Take the ground away, and their hair will start to stand up. Ask the volunteer to shake their head. g. Ask the volunteer to move their hand from the ball to their side, and to keep it there. Immediately ground the generator and then turn it off. h. The volunteer may step off the stool and touch elbows with a classmate to ground themselves of electrons. (Note: touching elbows will result in a static shock.) i. Note down observations. Part IV. Neon Indicator a. Turn the generator off and turn the knob counterclockwise. b. Detach the grounding sphere from the generator’s ground line and replace it with the neon indicator accessory. c. Turn the generator on and turn the knob clockwise. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering d. Point the neon indicator at the dome and slowly bring it closer without making contact. e. Bring it close enough for sparks to jump from the dome towards the accessory. f. Note down observations. Part V. Aluminum Helicopter Propeller a. Turn the generator off and turn the knob counterclockwise. b. Ground the generator with the grounding sphere. c. Attach the aluminum helicopter propeller accessory. d. Turn on the generator and slowly turn the knob clockwise. e. Note down observations. III. Results Part I. Making Sparks Observations: - When the grounding sphere was brought to proximity of the large dome, sparks started flying from the dome towards the grounding sphere. - There’s an apparent correlation between the distance of the grounding sphere from the large dome and the frequency of sparks. - As the grounding sphere is brought even more closer to the dome, the frequency of the sparks increased. Part II. Head of Plastic Hair Observations: - A while after the generator was turned back on, the plastic hairs on the accessory started to “float” on their own. - At the generator’s full capacity, the plastic hairs were able to stand up on their own. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering - When the professor reached his hand out towards the dome, the hairs of the accessory started dropping down back on their own. - The hairs start “floating” again once the professor’s hand was brought away from the dome. Part III. Human Hair Observations: - A while after the generator was turned on, the hair of the participant touching the generator started to stand up on their own. - After being instructed to shake their head, the hairs started standing up even taller than before. - When a classmate approached the participant, the classmate reached out their hand towards the standing hairs of the participant. What followed was the attraction of the participant’s hair towards the hand of the classmate. - The participant also held out their finger towards another classmate, which resulted in an audible spark that shocked both parties. - When the generator was turned off while the participant was still holding on to the generator’s dome, their hair dropped back down. Part IV. Neon Indicator Observations: - When the accessory came into close proximity of the dome, an audible “airy” sound can be heard, and sparks jumped from the dome towards the accessory. - The neon bulb grew brighter as it was brought closer to the dome, and it shines the brightest whenever there’s a spark between the two. The bulb momentarily shuts off after the spark before lighting up again. - The light emitted by the neon bulb was yellow in color. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Part V. Aluminum Helicopter Propeller Observations: - A while after the generator was turned on, the helicopter accessory started to spin slowly. - It kept accelerating as time progressed. - It spun in the opposite direction of where its blades were pointing at. IV. Discussions/Analysis Draw a neat, labelled diagram of the Van de Graaff generator. Hollow metal dome Metal brush Aluminum roller Insulating wall Rubber belt Motor Hand crank Metal brush Plastic roller Figure 1. Courtesy of Venerando Dayupay, Jr.[2] Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Discuss the principle, construction, and workings of the Van de Graaff generator. The Van de Graaff generator is an electrostatic generator that’s capable of creating a very large electrical potential at the surface of its dome in the order of a few million volts[3]. The generator is based on the principle of static electricity – that is, if a charged conductor is brought into contact with a conducting internal component of a hollow conductor, all the charges from the former will transfer over to the surface of the latter regardless of how much charge has accumulated in the hollow conductor. This explains why the generator is capable of generating high voltages at the surface of its dome[4]. A typical Van de Graaff generator consists of the following: one plastic roller fixed at the bottom of the generator, one aluminum roller fixed in the hollow metal dome, a rubber belt that travels over both rollers, and two metal brushes: one connected to the electric ground at the bottom, and the other electrically connected to the large dome. The reason behind the different use of materials for the rollers is so that one roller will become positively charged and the other negatively charged. The rollers gain their charges through the constant making and breaking of contact with the travelling rubber belt over them. The plastic roller on the bottom of the generator gains a positive charge, which aids in attracting negative charge by induction from the metal brush that’s connected to the electrical ground. The electrons from the ground are then attracted to the plastic roller but are stopped and collected by the travelling rubber belt, to which they are taken up the generator. The aluminum roller in the interior of the dome gains a negative charge, which is used in repelling the negative charge through induction collected by the rubber belt. Another metal brush is fixed and electrically connected to the large Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering dome, which is used in collecting the negative charge from the rubber belt. The repelling force from the aluminum roller force the electrons off the travelling rubber belt and is collected by the metal brush which is then conducted towards the dome. The dome accumulates the negative charge that was collected by the metal brush and in turn becomes negatively charged. Due to the principle of static electricity, it will constantly accumulate charge collected by the metal brush and spread it evenly across the surface. Eventually, the surface will not be able to hold anymore negative charge, and in turn the air surrounding the dome will ionize. Discuss the use of the Van de Graaff generator. Since the Van de Graaff generator can generate high voltages, it’s been historically used in the fields of particle physics where generators were used in accelerating subatomic particles like protons to study the collision when such particles hit their target[4]. This is in principle of how different charges interact with one another; like charges repel and opposite charges attract. Not only were Van de Graaff generators used in particle physics, but they were also used in the advancement of nuclear medicine and research, where generators were used as accelerators in order to produce intense particle and Xray radiation[5]. Insulators of the High Tension Tower, used for hanging electric cables, are either glass or porcelain discs or composite insulators using silicone rubber or ethylene propylene diene monomer (EPDM) rubber material, why are they selected to be a disc in shape? One important aspect that an insulator should do in high voltage applications is to maximize the creepage length, which is the shortest length along the surface of an insulator, between two insulated conductors. To do this, transmission line insulators are shaped as wide discs to maximize the creepage length between the conductors[6]. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Another important aspect of an insulator is that it should deter any possible conducting path around it between the conductors. All transmission lines are outdoors and are constantly exposed to the elements such as the rain, wind, and dust. Over time, these elements would deposit onto the insulators and create potential conducting paths between the conductors. In conjunction with being shaped like discs, they are also shaped like umbrellas as to encourage rainwater to wash the dirt off and flow off easily without depositing at the bottom of the insulators[6]. Discuss what will happen if a person touches a Van de Graaff generator. Consider all possible situations like charge of the sphere is too high or too low, or when the person is standing on an insulated platform or conducting platform while touching the sphere, etc. Several things can happen when a person touches a Van de Graaff generator depending on various conditions. When a person touches a Van de Graaff generator with a low charge, nothing much of note will happen. The charge generated is too small for the effects to be noticeable when that charge is transferred over to the person. However, there will be a big difference when the charge generated is too high, as the person touching it will get a painful shock from the sudden transfer of charge towards their body. If the person were to have touched the same generator while standing on an insulated surface, the charges would not travel throughout the body, but instead accumulate throughout. But when grounded, the charge will flow the body and out through the feet, where the person is in contact with the ground, or earth. Where are the electrons? Where the Van de Graaff generator gets its electrons is from the ground itself. The lower metal brush is connected to the electrical ground of the generator, where the attractive electric field of the plastic roller pulls in electrons from the Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering earth. The electrons are then transported up by the rubber belt, where it is collected by the upper metal brush and deposited into the generator’s dome. The grounding sphere of the setup is electrically connected to the earth as well. When the grounding sphere is brought close to the generator’s dome, sparks start flying from the dome towards the grounding sphere. Since the sphere is grounded, the natural tendency of negative electrical charges is to come back to the earth. As the earth is a wealthy reservoir of electrons, it is also a nearly boundless container of positive charge as well. The Van de Graaff generator essentially collects electrons from the ground and returns it back via the grounding sphere. What is making your hair stand on its end? What made my hair stand on its end is due to the amount of negative electrical charges I’ve accumulated from the Van de Graaff generator when I touch it with my hand. As the electrons are pushed into the generator’s dome, there will be a point where it could no longer hold any more electrons. When I placed my hand on the dome, the electrons were finally given a space where they can escape, to which consequently I collected and stored in my body. As my body get negatively charged from the incoming flow of electrons, so do the hairs on my body. As like charges repel, it’s only natural for the loose hair on my body to repel away from my negatively charged body and from each other. Theoretically, the hair of the volunteer should not come down even after the generator has been turned off. But this is contrary to your observation. Explain the reason. The location of where the experiment was conducted was not ideal and not recommended by the manuals provided to us students[7]. This is because during the summer, the climate of the Philippines is hot and humid. Moist air conduct electricity better than dry air, and that provided the correct conditions for the built- Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering up negative charge in the participant’s body to dissipate much quicker than expected, regardless of whether they were grounded or on an insulated surface. What caused a shock when the volunteer touched a fellow student? The shock was caused by a difference in electrical potential between the two students, where the volunteer had accumulated a high electrical potential whereas the other was grounded. Due to this difference, the natural order of the electrons from the participant was to jump towards the grounded student, and that’s what caused the spark. Why did your teacher ground the generator before allowing the volunteer to step off the plywood? This was so that the charges generated by the Van de Graaff generator head straight to the earth, making sure it was safe for the volunteer to remove their hand without accidentally shocking them with a spark. What happens with the frequency of the spark when you bring the grounding sphere closer to the dome? As noted down in the observations, the frequency of the spark increased as the grounding sphere was brought closer to the dome. The inverse can be said as well, as the frequency of the spark decreased as the grounding sphere was brought away from the dome. What is the role of the air gap between the grounding sphere and the dome? Air is a natural electrical insulator, and as the gap between two electrical fields increase, so does the resistance provided by the air increase. By bringing the grounding sphere and the generator’s dome closer together, the resistance from the air alone decreases, and eventually the resistance is low enough for sparks to start jumping between the two objects. It also explains why bringing the grounding sphere closer increases the frequency of the spark because the Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering resistance has gotten low enough for the voltage from the generator to catch up much quicker to form sparks. Why did the helicopter eventually rotate on its own? The helicopter is shaped in a particular way, such that its points are spiraling outwards from the center of the propeller. This shape is what propels the helicopter to spin on its own axis. Electrical fields are at its strongest at the highest amount of curvature[8]. And the force that an electrical field will exert on a point charge is directly proportional to the electric force it produces. Due to the points of the helicopter, the electric field is at its strongest at those points. Additionally, when the generator is turned on, the generator’s dome produces an electric field as it accumulates negative charge. Because the helicopter is also negatively charged due to the charges being sent directly into it from the generator’s dome, the tips also produce an electric field. Since the fields of both the helicopter and the generator’s dome are negative and they are in close proximity with each other, they repel each other in accordance with Coulomb’s law. The force then propels the helicopter in the opposite direction of where its electric fields are pointing. Explain your observation on the plastic hair. The same principle from why my hair stood up on its end can be applied to why the plastic hair stood on its own. As the negative charges build up on the generator’s dome, so do the plastic hairs of the accessory. As bodies with like charges repel, the plastic hairs started repelling away from the large dome of the generator, thus apparently floating on its own. Explain the concept of Coulomb’s Law in this experiment. Coulomb’s law state that like charges repel and opposite charges attract, and that force is directly proportional to the product of the charges and inversely proportional to the square of the distance between two charges[9]. This law has Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering been demonstrated by the hair-raising experiment, head of plastic hair experiment, and the aluminum helicopter experiment. For both the hair-raising and head of plastic hair experiment, each strand were negatively charged by the generator and started standing on their own because they were repelling one another. At a certain point, each strand reached an equilibrium where the forces of gravity and the forces of electrical repulsion balanced each other out, thus making it seem like they were floating mid-air. For the aluminum helicopter experiment, it generated strong electric fields at its tips that were repelling against another strong electric field produced by the generator’s dome. Since it was a repelling force, the force experienced by the helicopter was in the opposite direction of the electric fields from its spiraling tips. Explain the charging of conductors by induction. Charging by induction is an alternative way of giving a neutral conductor a charge at a distance. The process involves holding a negatively charged particle in proximity of a neutrally charged conductor. The negative charge from the particle repels the free electrons away from the neutrally charged conductor, and now the side of the conductor facing away from the charged particle is now full of electrons. Then, a ground wire is connected to the side, to which the electrons will freely move down to the earth due to the repelling force of the charged particle. Then, the wire is detached, and the charged particle is brought away from the conductor. What’s left in the conductor are positively charged atoms/molecules with missing electrons[9]. The concept revolves around the manipulation of the flow of electrons of a neutrally charged conductor through any charged particle that’s able to induce this force. The forced electrons then are grounded so that what’s left of the conductor are atoms with missing electrons, thus positively charging the conductor. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering Explain the charge distribution in the conductors (e.g., in the dome). The charge distribution in the dome as the generator is turned on is even throughout the surface. As more electrons are added into the dome, the additional electrons repel away from each other due to Coulomb’s law. Eventually, the dome will accumulate so many electrons, that the each of them will repel one another across the surface, evenly distributing the charge. Republic of the Philippines MINDANAO STATE UNIVERSITY – GENERAL SANTOS College of Engineering Department of Electrical and Electronics Engineering V. References [1] Chodos, A. (2011, February). February 12, 1935: patent granted for van de graaff generator. APS News. Retrieved May 24, 2023, from https://www.aps.org/publications/apsnews/201102/upload/February-2011.pdf. [2] Venerando Dayupay, Jr. Figure 1. [3] BYJU’S. (2023, February 3). Van De Graaff generator - working of Van de Graaff Generator: Byju’s. BYJUS. https://byjus.com/physics/van-de-graaff-generator/ [4] Unacademy. (2022, April 21). Working Principle of the Van de Graaff Generator. https://unacademy.com/content/neet-ug/study-material/physics/workingprinciple-of-the-van-de-graaff-generator/ [5] Van De Graaff generator: Definition and working principle. Turito. (2022, August 11). https://www.turito.com/blog/physics/van-de-graaff-generator [6] Holtzhausen, J.P. (n.d.). High Voltage Insulators (PDF). IDC Technologies. [7] Scientific Laboratory Supplies Ltd. © 2005-2023. (n.d.). Van de Graaff Generator Instructions - VDGPSUB. Scientific Laboratory Supplies Select Education. https://www.science2education.co.uk/handlers/libraryFiles.ashx?filename=Man uals_E_EDU2124_A.pdf [8] Physics tutorial: Electric fields and conductors. The Physics Classroom. (n.d.). https://www.physicsclassroom.com/class/estatics/Lesson-4/Electric-Fields-andConductors [9] Young, H. D. (2016). University Physics with Modern Physics (15th ed.). Pearson.
