GCSE Physics Static Electricity

electrically charged materials are brought together, they exert a force on each other. Materials with the same charge repel each other whereas materials with different charges attract each other. Current is the rate of flow of electrical charge. Electrical charge can easily flow through metals because they contain conduction (delocalised) electrons. These electrons are not confined to a single atom. This is the reason why metals are food conductors of electricity. Insulators cannot conduct electricity because all the electrons are held within atomsA charged body can be discharged safely by connecting it to earth with a conductor (e.g. a metal wire) (We say that the conductor is earthed). If the body is positively charged, electrons will transfer from the conductor to the body. So the conductor becomes positively charged because it loses electrons. If the body is negatively charged, electrons transfer to the conductor from the charged body. So the conductor becomes negatively charged as it gains electrons. The conductor can only hold charge if it is insulated (isolated) from the ground- otherwise the conductor won’t hold any charge because of electron transfer between the conductor and ground.The greater the charge on an isolated body the greater the potential difference between the body and earth. If the potential difference becomes high enough, a spark may jump across the gap between the body and any earthed conductor which is brought near it. This can be dangerous. Uses of Static Electricity: In a photocopier, an image plate is given a positive charge. An image of the page to be copied is projected onto the charged plate. When light falls on to the plate, the charge leaks away on the “whiter” sections of the plate, leaving a pattern of the image. Negatively charged black ink powder is attracted to the remaining positively charged sections of the plate, which is transferred onto positively charged paper. The paper is heated so that the powder melts and sticks to it, producing a hard copy of the original page. Electrostatic Precipitators: Coal-fired power stations produce vast quantities of ash and dust. Electrostatic precipitators remove this material from the flue gases before they get into the atmosphere. The particles of gas and dust pass through a grid of wires in the precipitator. The grid wires are negatively charged and so the particles become negatively charged when they touch the wires. The negatively charged ash and dust particles are attracted onto the positively charged metal plates which are positioned either side of the grid of wires. The plates are shaken at intervals so that the ash and dust drop to the floor of the precipitator, where the particles are removed. Electrostatic Paint Sprayers: Automatic paint sprayers are used to paint metal panels. The spray nozzle is connected to the positive terminal of an electrostatic generator. As the paint droplets pass through the spray nozzle, they all pick us a positive charge and so repel each other, spreading out to give an even layer of paint. The negative terminal is connected to the metal panel, giving the metal panel a negative charge. Therefore, the positively charged paint droplets are attracted to the metal panel. Dangers of Static: Pipe Problems: When a road tanker pumps oil or petrol into a storage tank, the connecting pipe must be earthed. If it isn’t, the pipe could become charged. A build up of charge would cause a spark. This could cause an explosion as the fuel vapour reacts with oxygen in the air. Antistatic Floors: To eliminate static charge in operating theatres, an antistatic material is used for the floor surface. This material is a poor electrical conductor so it conducts charge to Earth.