Feb16 - PHYS142 Lecture 18 Magnetic Fields Chapter 29 All...

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Magnetic Fields • Chapter 29 All sections except 6 29.1 Magnetic Fields and Forces 29.2 Motion of a Charged Particle in a Uniform Magnetic Field 29.3 Applications Involving Charged Particles Moving in a Magnetic Field 29.4 Magnetic Force Acting on a Current-Carrying Conductor 29.5 Torque on a Current Loop in a Uniform Magnetic Field PHYS142 Lecture 18 1
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What’s coming next? Chap. 23 Electric field Chap. 24 Gauss’s law Chap. 25 Electric potential Chap. 26 Capacitance and dielectrics Chap. 27 Current and resistance Chap. 28 Direct-current circuits Chap. 29 Magnetic fields Chap. 30 Sources of magnetic fields Chap. 31 Faraday’s law Chap. 32 Inductance Chap. 33 Alternating-current circuits 2
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A magnet, such as a compass has a north (N) and a south (S) pole. S If the magnet is free to rotate, its N-pole will point towards the Earth’s geographic north pole and its S-pole will point towards the Earth’s geographic south pole. N Magnetic poles: Magnetic fields and forces (29.1) 3
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An important rule in magnetism: “Opposite poles attract, like poles repel. N S N S N S N S 4
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Magnets produce/generate magnetic fields (Chap. 30) The magnetic field is a vector quantity The letter B is used to denote the magnetic field How to determine the direction of the magnetic field at any point in space? We place a small ( imaginary ) compass at the point of interest. The direction of the magnetic field at that point is the direction in which the N-pole of the compass points. Magnetic fields 5
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Example 1 : Determine the direction of the B-field at point P magnet P S N Since unlike poles attract the compass will rotate until its S-pole is near the N-pole of the magnet. The direction of the B-field at point P is given by the direction of the N-pole of the compass. Place the small compass at point P S N P S N B 6
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Using a compass we can draw the magnetic field lines of a magnet. 7 Magnetic field line
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N S N S N S Magnetic field inside the magnet If we cut the magnet in half we get two magnets. An imaginary compass placed between the two magnets gives the direction of the B-field inside the magnet.
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This note was uploaded on 02/22/2011 for the course PHYS 142 taught by Professor Altounian during the Spring '07 term at McGill.

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Feb16 - PHYS142 Lecture 18 Magnetic Fields Chapter 29 All...

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