7-MAGNETIC INDUCTION1

7-MAGNETIC INDUCTION1 - MAGNETIC FIELDS AND INDUCED EMF...

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MAGNETIC FIELDS AND INDUCED EMF Purpose: To investigate the EMF created by a varying magnetic field in a coil. Equipment: Rotating rod from centripetal force lab, magnet, coils, PASCO interface and computer, voltage sensor, vernier magnetic field sensor. Background: Electromotive Forces (EMF) convert one form of energy to others which we consume daily. We recognize the devices that supply power as batteries, photo-voltaic cells, thermocouples, and generators. All EMFs can produce a potential difference between two points, commonly called terminals. The high potential terminal is denoted with a + sign, and the low potential terminal is denoted with a - sign. When the terminals are connected to a circuit the potential difference causes any free charges within the circuit to move, thereby doing work on the charges. We measure the work an EMF can perform in volts, work per unit charge. The important property of the EMF is that it can produce a potential everywhere in the circuit and can produce a current. Circuit Figure 1. A loop of wire in a magnetic field that is directed into the page. Changes in the size of the loop, orientation of the loop, or magnetic field strength will produce an EMF in the circuit while those changes are occurring. We know that EMF ’s can be created by chemical means from our everyday use of batteries. And, as we know, batteries have limitations on the length of time the potential difference can be maintained and the size of the potential difference. Magnetic fields and conductors can produce EMF’s of varying strengths. Consider a loop that is connected to a circuit component, like that of figure 1, and is centered in a magnetic field. Changes in dimension of the loop will cause a current to be produced. Likewise, if the magnitude of the magnetic field should change and the size of the loop is constant, a current will also be produced. In either case, the charges in the conductor feel the presence of the magnetic field. When the loop changes size or the magnetic field changes strength, the flux through the loop changes. It is this change in flux that induces the EMF in the loop. Remember that flux is defined as the number of field lines that pass through a cross sectional area. If the area changes or the magnetic field changes in time then the flux through the loop has changed. The change in flux produces an EMF which is given by
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7-MAGNETIC INDUCTION1 - MAGNETIC FIELDS AND INDUCED EMF...

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