PY208-Lecture-18 - Physics 208N-004 Lecture #18 23 February...

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1 Physics 208N-004 Lecture #18 – 23 February 2011 Chapter 28: 1-3 – Sources of Magnetic Fields Summary Chapter 27 Magnets have north and south poles. Like poles repel, unlike attract. Unit of magnetic field: tesla (T) Electric currents produce magnetic fields. A magnetic field exerts a force on an electric current: A magnetic field exerts a force on a moving charge: Torque on a current loop: Magnetic dipole moment: The torque on a current carrying loop: The quantity NIA is called the magnetic dipole moment, μ : 27-5 Torque on a Current Loop; Magnetic Dipole Moment The potential energy of the loop depends on its orientation in the field: Example 27-11: Torque on a coil. A circular coil of wire has a diameter of 20.0 cm and contains 10 loops. The current in each loop is 3.00 A, and the coil is placed in a 2.00-T external magnetic field. Determine the maximum and minimum torque exerted on the coil by the field.
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2 27-6 Applications: Motors, Loudspeakers, Galvanometers An electric motor uses the torque on a current loop in a magnetic field to turn magnetic energy into kinetic energy. The use of brushes and a commutator switch the direction of the current so that the torque on the loop acts to rotate it in the same direction on each half cycle. 21.(II) For a particle of mass m and charge q moving in a circular path in a magnetic field B , ( a ) show that its kinetic energy is proportional to the square of the radius of curvature of its path, and ( b ) show that its angular momentum is about the center of the circle.
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PY208-Lecture-18 - Physics 208N-004 Lecture #18 23 February...

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