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Magnetism (sec. 27.1) Magnetic field (sec. 27.2) Magnetic field lines and magnetic flux (sec. 27.3) Motion of charges in a B field (sec. 27.4) Applications - moving charged particles (sec. 27.5) Magnetic force on conductor with current (sec. 27.6) Force and torque on a current loop (sec. 27.7) Direct current motor(sec. 27.8) The Hall effect(sec. 27.9) Magnetic Field & Forces Ch. 27 C 2009 J. Becker

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Forces between bar magnets (or permanent magnets )

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Earth’s magnetic field (Note the N-S polls of magnet!)

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Compass over a horizontal current-carrying wire

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Magnetic force acting on a moving (+) charge

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Magnetic field lines associated with a permanent magnet, coil, iron-core electromagnet, current in wire, current loop

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MAGNETIC FLUX through an area element dA

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Orbit of a charged particle in a uniform magnetic field is a circle R = m v / q B

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The Van Allen radiation belts around the Earth

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Velocity selector for charged particles uses perpendicular E and B fields q v B = q E v = E / B

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Mass spectrometer uses a velocity selector to produce particles with uniform speed. And from R = m v / q B we get q / m = v / B R

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Force on a moving positive charge in a current-carrying conductor: F = I L x B L I I For vector direction use “RIGHT HAND RULE”

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Magnetic force on a straight wire carrying current I in a magnetic field B Right hand rule F = I L x B

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Magnetic field B, length L, and force F vectors for a straight wire carrying a current I

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Components of a loudspeaker F = I l x B

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Forces on the sides of a current-carrying loop in a uniform magnetic field. This is how a motor works!

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Right hand rule determines the direction of the magnetic moment ( ) of a current-carrying loop

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Torque ( x B) on this solenoid in a uniform magnetic field is into the screen thus rotating the solenoid clockwise

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Current loops in a non-uniform B field

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Atomic magnetic moments in an iron bar (a) unmagnetized (b) magnetized (c)Torgue on a bar magnet in a B field

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Bar magnet attracts an unmagnetized piece of iron; the B field gives rise to a net magnetic moment in the object

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A simple DC motor

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The Hall effect – forces on charge carriers in a conductor in a B field. With a simple voltage measurement we can determine whether the “charge carriers” are positive or negative.

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A linear motor

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Electromagnetic pump

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See www.physics.edu/becker/physics51 Review C 2009 J. F. Becker

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