Chap27_Notes

# Chap27_Notes - Physics 184 Physics for Scientists Engineers...

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10/15/2011 Physics for Scientists & Engineers 2 1 Physics 184 Physics for Scientists & Engineers 2 Fall Semester 2011 Chapter 27: Magnetism

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Exam 2 Summary Problem 1 2 3 4 5 6 7 % 92 66 63 81 71 78 58 10/15/2011 Physics for Scientists & Engineers 2 2 0 20 40 60 80 100 0 5 10 15 20 25 30 35 40 Number of students Score (%) 0 20 40 60 80 100 0 5 10 15 20 25 Score (%) Avg. = 75.4%, st. dev. = 19.4%
10/15/2011 Physics for Scientists & Engineers 2 3 Permanent Magnets - Poles Magnets exert forces on one another --- attractive or repulsive depending on orientation. Demo If we bring together two permanent magnets such that the two north poles are together or two south poles are together, the magnets will repel each other If we bring together a north pole and a south pole, the magnets will attract each other

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10/15/2011 Physics for Scientists & Engineers 2 4 Magnetic Field Lines Permanent magnets interact with each other at a distance, without touching In analogy with the electric field, we define a magnetic field to describe the magnetic force As we did for the electric field, we may represent the magnetic field using magnetic field lines The magnetic field direction is always tangent to the magnetic field lines Demo
10/15/2011 Physics for Scientists & Engineers 2 5 Magnetic Field Lines (2) The magnetic field lines from a permanent bar magnet are shown below Two dimensional computer calculation Three dimensional real-life

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10/15/2011 Physics for Scientists & Engineers 2 6 Broken Permanent Magnet If we break a permanent magnet in half, we do not get a separate north pole and south pole When we break a bar magnet in half, we always get two new magnets, each with its own north and south pole Unlike electric charge that exists as positive (proton) and negative (electron) separately, there are no separate magnetic monopoles (an isolated north pole or an isolated south pole) Scientists have carried out extensive searches for magnetic monopoles; all results are negative Magnetism is not caused by magnetic particles! Magnetism is caused by electric currents
10/15/2011 Physics for Scientists & Engineers 2 7 Magnetic Field Lines For the electric field , the electric force points in the same direction as the electric field and the electric force was defined in terms of a positive test particle However, because there is no magnetic monopole , we must employ other means to define the magnetic force We can define the direction of the magnetic field in terms of the direction a compass needle would point A compass needle, with a north pole and a south pole, will orient itself in equilibrium such that its north pole points in the direction of the magnetic field Thus the direction of the field can be measured at any point by moving a compass needle around in a magnetic field and noting the direction that the compass needle points

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10/15/2011 Physics for Scientists & Engineers 2 8 Clicker Quiz: Break a Permanent Magnet in Two If we break a permanent magnet in half, what do we get?
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## This note was uploaded on 02/03/2012 for the course MTH 235 taught by Professor Staff during the Fall '11 term at Michigan State University.

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Chap27_Notes - Physics 184 Physics for Scientists Engineers...

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