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# lab35 - LAB 35 MAGNETIC FIELD OF A CURRENT-ELECTROMAGNETIC...

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LAB# 35: MAGNETIC FIELD OF A CURRENT-ELECTROMAGNETIC INDUCTION INTRODUCTION: In 1820 Hans Christian Oersted discovered during the course of a physics demonstration for his students 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 Faraday in England and Henry in the United States. Their experiments can be summed up as: an emf, (electro-motive force) is induced in a conductor whenever there is a change in the magnetic flux linked with the conductor. This change of flux can be produced in several ways for example moving one conductor near a current-carrying 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 Δφ , and the time Δτ required to produce this change. The average induced emf ε is given by: ! = " N # \$ # % (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 and 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

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lab35 - LAB 35 MAGNETIC FIELD OF A CURRENT-ELECTROMAGNETIC...

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