lab_35

# lab_35 - LAB 35 MAGNETIC FIELD OF A INDUCTION INTRODUCTION...

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LAB# 35 MAGNETIC FIELD OF A CURRENT- ELECTROMAGNETIC INDUCTION INTRODUCTION: In 1820, Hans Christian Oersted discovered that there is a magnetic field associated with an electric current. The reverse effect that an electric current might be caused by a magnetic field was developed in 1831 by Michael Faraday in England and Joseph Henry in the United States. Their experiments can be summed up as follows: an emf, (electro- motive force) is induced in a conductor whenever there is a change in the magnetic flux going through the conductor. This change of flux can be produced in several ways. For example, when a conductor moves in the presence of a magnetic field with changing velocity; a current is thereby induced on the conductor. The generation of an emf by this process is called electromagnetic induction. If the emf is induced in a conductor that is part of a closed circuit, there will be an electric current induced in that circuit. The emf induced in a circuit is found to depend only upon the number of turns N in the circuit, the change in the magnetic flux d B , and the time d required to produce this change. The average induced emf is given by: dt d N B (1) The induced current developed by electro-magnetic induction is in such a direction as to oppose (by its magnetic action) the change inducing the current. This is why a negative sign is introduced into equation 1 (above). This equation is the principle of Lenz’s Law is a good example of the conservation of energy. An induced current can produce heat or do either chemical or mechanical work. The energy must come from the work done in inducing the current. When induction is due to a change of magnetic flux from one coil (the "primary") that links another coil (the "secondary") work must be done to compensate for this change in flux. The energy of the induced current is derived from the work done in order to produce the change of flux. Hence, the induced current in the

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lab_35 - LAB 35 MAGNETIC FIELD OF A INDUCTION INTRODUCTION...

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