Presentation on theme: "Static Charge -and- Van de Graaff Generators What is Static Charge? Here, we're talking about charge as the difference in the number of electrons that."— Presentation transcript:
Static Charge -and- Van de Graaff Generators What is Static Charge? Here, we're talking about charge as the difference in the number of electrons that two different objects have. When the atoms of one object give up or lose their electrons, these electrons end up somewhere else. Another object picks up or gains these strays. Since electrons are negatively charged, and protons are positively charged, an object that has picked up electrons without picking up protons will have a negative charge overall. When two objects made of very different materials are rubbed together, one will be more likely to give away its electrons. The other will be more likely to accept these electrons. The more you rub, the more electrons jump from one to the other. Where can you find it? Large build-ups of electrons can give away their presence in other ways. Since similar charges repel each other and opposite charges attract, you can see negatively charged objects repelling each other and clinging to positively charged objects. If you stick two pieces of tape to a smooth surface, then quickly peel each off, the electrons on the non- sticky sides of the tape will try repel each other If you slide down a plastic playground slide quickly in cotton clothing, the negative charges on your hair will repel each other and your hair will stick up. (For best results, make sure the air is dry) How do you know it is there? Once an object has gained electrons, it will want to return to its neutral state and have just as many protons as electrons. If enough electrons jump from your skin to another object at once you can feel a shock, hear a zap, or see a small spark. Many times, however, the charge built up is too small for humans to notice without help. A tool called a voltmeter can measure how many more electrons are on object than are on its neighbour. The electron got it’s name when a scientist noticed particles clinging to what material after he rubbed it with rabbit’s fur? (Hint: Its Greek translation is ‘elektron’) a. rubber b. amber c. iron d. aluminium Number the items below from most likely to donate electrons (1) to most likely to accept electrons (7) Lightening is a large-scale example of electrons jumping from one place to another. Where does the extra build up of electrons come from? a. Rain droplets collide with each other as they fall, knocking off electrons b. As layers of air of different temperatures rub together, the cooler layer donates electrons c. Pockets of rising moisture lose electrons when hit by falling ice and sleet d. Clouds bump into each other, knocking off electrons STEEL Fur
Van de Graaff generator The Van de Graaff generator was invented by Robert J. Van de Graaff in 1929 at Princeton University. One of the largest can generate 2 million volts (XX electrons) and uses metal spheres that are each 15 feet across. Van de graff generators come in all sorts of sizes and can use similar materials to get the same job done. They can produce anywhere from (number) to (number)! http://www.engr.uky.edu/~gedney/courses/ee468/expmnt/vdg-graph.gif
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