PY208-Lecture-17

# PY208-Lecture-17 - Physics 208N-004 Lecture#17 21 February...

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1 Physics 208N-004 Lecture #17 – 21 February 2011 Chapter 27: 4-6 – Magnetic Forces and Torques Review Sources of Magnetic Fields are: (1) Currents (2) Time Varying Electric Fields (dE/dt) Magnetic Fiels are Dipole Fields Magnetic Declination Magnetic Dip Unit of B : the tesla, T: 1 T = 1 N/A·m or the gauss, G : 1 G = 10 -4 T The force on a moving charge is related to the force on a current: Once again, the direction is given by a right-hand rule. Remember F = I l x B , where I = Nq/t and l = v t for a single charge, F = ( q/t ) ( v t ) x B F = q v x B F = ( q/t ) ( v t ) x B

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2 27-4 Force on an Electric Charge Moving in a Magnetic Field Conceptual Example 27-4: Negative charge near a magnet. A negative charge - Q is placed at rest near a magnet. Will the charge begin to move? Will it feel a force? What if the charge were positive, + Q ? 27-4 Force on an Electric Charge Moving in a Magnetic Field Example 27-5: Magnetic force on a proton. A magnetic field exerts a force of 8.0 x 10 -14 N toward the west on a proton moving vertically upward at a speed of 5.0 x 10 6 m/s (a). When moving horizontally in a northerly direction, the force on the proton is zero (b). Determine the magnitude and direction of the magnetic field in this region. (The charge on a proton is q = + e = 1.6 x 10 -19 C.)
3 27-4 Force on an Electric Charge Moving in a Magnetic Field Example 27-6: Magnetic force on ions during a nerve pulse. Estimate the magnetic force due to the Earth’s magnetic field on ions crossing a cell membrane during an action potential. Assume the speed of the ions is 10 -2 m/s. If a charged particle is moving perpendicular to a uniform magnetic field, its path will be a circle. 27-4 Force on an Electric Charge Moving in a Magnetic Field

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4 27-4 Force on an Electric Charge Moving in a Magnetic Field Example 27-7: Electron’s path in a uniform magnetic field.
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PY208-Lecture-17 - Physics 208N-004 Lecture#17 21 February...

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