Lecture 15 Ch28

# Lecture 15 Ch28 - PH 222-3A Spring 2007 222 3A Magnetic...

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H 222- A Spring 2007 PH 222 3A Spring 2007 Magnetic Field Lecture 15 Chapter 28 (Halliday/Resnick/Walker, Fundamentals of Physics 8 th edition) 1

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Chapter 28 Magnetic Fields In this chapter we will cover the following topics: Magnetic field vector, Magnetic force on a moving charge, B G B F G Magnetic field lines Motion of a moving charge particle in a uniform magnetic field Magnetic force on a current-carrying wire Magnetic torque on a wire loop Magnetic dipole, magnetic dipole moment all effect μ G Hall effect Cyclotron particle accelerator 2
One can generate a magnetic field using one of the l l i thd What Produces a Magnetic Field following methods: Pass a current through a wire and thus form what is known as an "electromagnet." se a "permanent" ma net Use a permanent magnet. Empirically we know that both types of magnets attract small pieces of iron. Also, if suspended so that they can rotate freely they align themselves along the north-south direction. We can thus say that these magnets create in the surrounding space a " " , which manifests itself by exerting a magnetic force . B B F magnetic field G G We will use the magnetic force to define precisely the magnetic field vector . B G 3

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The magnetic field vector is defined in terms of the force it B F Definition of G G B B Fq v B = × G G G sin B v B φ = exerts on a charge , which moves with velocity . We inject the charge in a region where we wish to determine qv q G G at ndom directions trying to scan all th possible directions B random directions, trying to scan all the possible directions. There is one direction for which the force on is zero. This direction is parallel with . For all other directions is B B BF G GG not zero, and its magnitude where is the angle between and In addition, is perpendicular to the plane defined sin B B vB F v B = G G by The magnetic force vector is given by the equation B v G The defining equation is sin . B v B q v B I unit of : G The defining equation is . If we shoot a particle with charge = 1 C at right angles ( 90 ) to with speed = 1m/s and the B q Bv SI unit of G B magnetic force 1 N, then = 1 tesl B FB = 4 An earlier (non-SI) unit for B, still in common use, is the gauss (G) 1 tesla= 10 g s a. aus G 4
he vector product of the vectors and a b a b The Vector Product of Two Vectors GG G The vector product is a vector . The magnitude of is given by the equation ca c c = × G G The direction of is perpendicular sin . c b φ = G to the plane defined y the vectors and P b G G by the vectors . The sense of the vector is given by the : Place the vectors and tail to tail. ab c right -hand rule a. G G G Rotate in the plane along the shortest aP b. G angle so that it coincides with . Rotate the fingers of the right hand i the same direction b G Rotate the fingers of the right hand in the same direction.

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## This note was uploaded on 09/26/2008 for the course PH 222 taught by Professor Mirov during the Spring '08 term at University of Alabama at Birmingham.

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Lecture 15 Ch28 - PH 222-3A Spring 2007 222 3A Magnetic...

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