Van de Graaff Generator Aim: To observe static electricity using a Van der Graaff generator Keywords: Electrons: A negatively charged particle Proton: A positively charged particle Neutron: A neutrally charged particle. This lesson we were shown a demonstration of a Van der Graaff generator. There were five specific demonstrations shown and they can be seen in the videos and images below. The first demonstration can be seen in the video “How a Van der Graaff generator works” below. This video explains how a Van der Graaff generator generates its electricity. The belt that can be seen in the video is revolving around two plastic pulleys. The negative charges or electrons are rubbing off of the pulleys onto the belt, causing the pulleys to become positively charged. Due to the fact that opposite charges attract each other, any negative charges on the metal spikes attempt to cross to the pulley, because of its positive charge. However, instead of reaching the pulley, the electrons are collected on the belt, before being brought up to the metal dome at the top of the generator. Once here, the charges have nowhere else to go, so they build up as “static electricity.” However, once thee small ball comes within the electric field, all of the electrons jump the gap at once, creating the “miniature lightning bolt” that can be observed. In the second demonstration, a metal rod with strands of fabric on the end was attached to the top of the generator. Once enough charge had built up, the electricity would flow into the fabric, causing each strand to become negatively charged. Due to the fact that they all have the same charge, each strand is repelled from each other and the generator, meaning that they appear to stand on end. The third demonstration involved a container filled with metal balls that had been coated in graphite powder, which was attached to the top of the generator. When the electricity passed into the container, it had a similar effect to the fabric. Each ball being negatively charged, caused them to repel each other, and levitate inside the container. In the fourth demonstration, a stack of foil cups was placed on top of the generator. Once enough electrons had built up, the repulsion caused the cups to fly off the top one at a time. The final demonstration, involved a two plastic tubes. One held an exposed wire connected to a light at the other end, and the other was filled with a gas. When the tube with the exposed wire was placed within the electric field of the generator, the light would activate. The second demonstration, with the tube hold gas, was wired by one end to the smaller conducting ball, and the other end to the tap, which acted as the earthing point. When enough charge passed through to the conducting ball, it flowed down the wire, into the tube, activating the gas and causing it to glow. This diagram below shows the flow of electrons when a person comes into contact with a Van der Graaff generator. The electrons that build up in the dome of the Van de Graaff generator, flow when a conductor is within their electric field. If someone touches the dome of the generator, then all the electrons will flow down their arm and into their body. Once the electrons are in the person’s body, they will eventually reach the person’s head. This means that all the hairs on the person’s body become negatively charged. Similar to the demonstration with the fabric, the hairs will repel each other and therefore stand on end. Note, that the energy stored within the person is “static” meaning that it is unable to flow anywhere. This is due to the foam mat that the person is standing on being a poor conductor or “insulator” of electricity. If the electricity was allowed to flow to earth, then this would shock the person, giving them an electric shock, so powerful, it could possibly kill them. Lesson Summary:
Learnt how a Van de Graaff generator builds its electrical charge. Observed repulsion in action, through the demonstration with the cups and fabric Observed how attraction can cause energy to jump across air gaps
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