CAC - Noticias

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WHAT YOU ALWAYS WANTED TO KNOW ABOUT... ELECTRICITY Posted: 16 Mar 2012 12:18 AM PDT Today, the 16th March, is the 223rd anniversary of the birth of German physicist Georg Simon Ohm, who discovered one of the fundamental laws of electricity. And we’ve been talking about electricity with Vicente Pelegero, head of Education and Scientific Creativity, who loves telling people about science and making it accessible and interesting, so that we all understand it better. His ideas are then translated into interactive modules and experiences that explain to visitors some of the scientific concepts in the Science Museum’s various exhibitions. Today he has been with a team from Belgium’s “één” state-owned TV channel, who are in Valencia for the Fallas Festival, to tell them about the educational events and activities that visitors can find at the City of Arts and Sciences, including the amazing Theatre of Electricity at the Science Museum, one of the most popular visitor workshops. In it, they discover the Tesla Coil which is named after its inventor and which allows visitors to see, listen and even smell electrical discharges resembling rays of lightning. It is 223 years since the birth of the German physicist Georg Simon Ohm, who discovered the basic law that bears his name and that underlies all the laws of electricity. Indeed, a unit of electrical resistance is called an ohm. What is Ohm’s Law? Why is it so important? Ohm was the first to realise that a cable’s electrical resistance depends on its characteristics: the type of material, its length or its parameter. His most significant contribution to science was the law that bears his name, which establishes that there is a relationship between the total resistance of a circuit, the electrical current and the voltage. This law is applicable to all electrical circuits. Just think for a moment about things that run on electricity: household appliances, computers, vehicles and even pacemakers… they are all governed by Ohm’s Law. What is static electricity? In the Science Museum, one can see this phenomenon at the Theatre of Electricity. Why do we sometimes get electrical shocks when we open a car door or touch someone? As you know, there are two types of electrical discharge: positive and negative. Things around us are usually neutral: they have the same amount of positive and negative charges. With a simple experiment, we can understand why these annoying little shocks occur. We get a balloon and rub it with a woollen cloth. As we do so, some of the electrical charges from the balloon pass into the wool, so that the wool is now charged. We can now attract little pieces of paper to it or even stick the balloon to the wall. Well, something similar happens when we get out of the car seat: as our back rubs the seat, the charge passes to us. When we then touch the vehicle (which is metal and therefore a great conductor) we quickly discharge electricity and feel that discharge as an electrical shock. Is it true that you even make visitors’ hair stand on end? Yes, by using a Van der Graaf generator we can charge an insulated person, which is more practical than rubbing and rubbing… Because the same types of charge repel each other, our volunteer’s hair tends to separate. Because hair is so light, it literally stands on end. This generator can charge a person with up to 200,000 volts, which is huge. Remember that in our homes the electrical current is 220 volts! But is the volunteer safe? Why doesn’t he or she get an electrical shock? As I said, the volunteer is insulated. If she were not standing on a plastic stool when the Van der Graaf machine is switched on, the charges would go through her to the floor and she’d get a shock. And what about the Tesla Coil? Why is called that? Who was Tesla? It was named after its inventor, Nicolas Tesla. He was a visionary: many of his ideas became a reality. It is thanks to his electrical motor that electricity came into general use. Others, however, did not materialise. The Tesla Coil was originally created to turn one of his obsessions into a reality: to transmit electrical currents without the use of cables. Sadly, he never succeeded. It is now used to generate the high voltage needed to produce electrical rays more than 1 metre long. Why is it inside a cage? The cage forms a physical barrier that protects us from the electrical rays. Because it’s metal, it’s a good conductor of electricity. When the ray of electricity collides against the cage, the charges flow through a cable down to the earth underneath the Museum, and there they dissipate. Even though we don’t see them, the cage also protects us from the powerful electromagnetic fields created by the Tesla: they could switch on fluorescent strip lights from 15 metres away. Are the rays produced by the Tesla the same as those of lightning? When there is flash of lightning, the air heats up to around 28,000 ºC in a fraction of a second. This is five times hotter than the surface of the Sun! This rapid change of heat makes the air literally explode producing a shock wave: thunder. Our rays are produced in the same way: an enormous difference in electrical power. Visitors can see the electric arc, listen to the thundering sound and smell the characteristic odour of ozone. Doesn’t that smell remind you of something? Yes, of a storm.

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