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Lesson 17: Linking Electricity to Magnetism As you just learned in the previous lesson, the magnetic field of a magnet basically comes from the spinning of electrons in atoms. This is a relatively recent theory, and certainly did not help scientists hundreds of years ago when they were first trying to figure out why magnets were magnets. One of the few hints they had was that electric and magnetic fields did seem to be quite similar. The breakthrough came in 1820 when Hans Christian Oersted performed a series of public experiments that showed how electric current could affect magnets. At first, things didn't work too well in the demo since the wire was being held parallel to the compass that was being used. More by accident than anything, the wire was eventually held perpendicular to the wire. This resulted in the compass spinning to point in a different direction. The conclusion was that the current flowing through the wire caused a magnetic field to be formed around the wire. We will say that the current flowing through the wire induced a magnetic field. To keep track of the direction of the magnetic field around the wire, we use a series of rules based on holding your hand in certain positions. In all of these rules we will be using different parts of your hand since they are perpendicular to each other, just like the results Oersted had in his experiments. No matter which rule you are using first make the choice of which hand you are supposed to be using: Electrons, electron current flow, or anything negative → left hand Protons, conventional current flow, or anything positive → right hand We will assume that the current flowing through the wire is “electron flow” unless we have a good reason to think otherwise. In this model, the flow of charges through the wire is made up of electrons. When we draw diagrams for the following rules, we often do it using simple arrows as symbols of the directions involved. Since some of the directions will sometimes be in and out of the page, we will use two special symbols. The first is a circle with a dot. It is supposed to look like the tip of an arrow coming out towards you. It shows a vector coming out of the page. The second is a circle with an X. It is supposed to look like the feathers of an arrow going away from you. It shows a vector going into the page. 7/20/2008

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