1102_Exp09_Lenz_Law - NAME_ Station Number _ LAB PARTNERS_...

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1 NAME__________________________ LAB PARTNERS____________________ Station Number ___________________ __________________ Electromagnetic Induction: Faraday’s Law and Lenz’s Law Experiment 9 INTRODUCTION A changing magnetic field can produce a potential difference, often called an emf , across a coil of wire. If the coil is part of a closed circuit, a current is induced in the circuit. The changing magnetic field can be produced by relative motion between a coil and a permanent magnet or by changing the current in one coil that is placed near another coil. Effects of these kinds are known as electromagnetic induction and can be described by Faraday&s law and Lenz&s law. Motors, generators, and transformers are a few of the many common devices whose operation is explained by the laws of electromagnetic induction. In this experiment, a coil passes through a magnetic field, causing a change in the magnetic flux in the coil. The induced emf in the coil and the effect of the induced current on the coil&s motion are studied. THEORY Faraday&s law of induction states that the magnitude of the induced emf is related to the change in magnetic flux according to , i f i f t t N t N emf Φ Φ = Φ = (1) where Φ is the magnetic flux, N is the number of turns in the coil, t is the time, and f and i mean final and initial, respectively. The magnetic flux for a constant magnetic field B is given by θ cos A B = Φ , ( 2 ) where A is the area of the loop through which the field lines pass, and is the angle between the magnetic field and the line normal to the plane of the loop. In this experiment, a coil at the end of a pendulum will swing through a region of space with magnetic field. As the coil enters this region, the magnetic flux, Φ , through the coil increases and an emf is induced according to Eq. (1). The emf induced in the coil causes a current that produces a magnetic field to oppose the change in flux, this is Lenz&s Law. The orientation of the induced magnetic field will be opposite to the orientation of the field between the magnets producing a repulsive magnetic force that slows down the pendulum.
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2 Figure 1 During the experiment, the coil will be connected in the circuit shown in Figure 2.
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This note was uploaded on 09/15/2010 for the course PHYS 1102 taught by Professor Lowellwood during the Spring '10 term at University of Houston.

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1102_Exp09_Lenz_Law - NAME_ Station Number _ LAB PARTNERS_...

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