18 - Fields from Currents

# 18 - Fields from Currents - PHYS 212 Fall 2009 Fields Due...

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PHYS 212 Fall 2009 Fields Due to Currents 10/5/09

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Summary F = q E + q v × B Force on a charge Force on a wire F = i L × B Torque on a current loop τ = μ × B μ = Ni A p Electric Dipole Magnetic Dipole Q - Is a current loop a dipole magnet?
Torque Example A coil of wire has an area of 2.0E-4 m 2 , consists of 100 loops or turns, and contains a current of 0.045 A. The coil is placed in a uniform magnetic Feld of 0.15 T. (a) Determine the magnetic moment of the coil. (b) ±ind the maximum torque that the magnetic Feld can exert of the coil. μ = Ni A μ = 100(0.045 A )(2.0 E 4 m 2 ) = 9.0 E Am 2 (a) Magnetic moment is normal ( ) to the coil Maximum torque is when magnetic moment is perpendicular to B τ = × B = B sin θ (b) = (9.0 E Am 2 )(0.15 T ) = 1.4 E Nm Am 2 ( ) ( T ) = Am 2 ( ) ( N C m ) = Am 2 ( ) ( N C ( ) m ) = Nm Units:

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Magnetic Fields from Currents Discovered by Hans Christian Oersted (1777-1851) A current carrying wire creates a magnetic ±eld (de²ects a compass) Compass “maps out” ±eld lines - circular Right Hand Rule 2: Curl ±ngers in a half circle. Point thumb in the direction of the current, and ±ngers will point in the direction of the magnetic ±eld.
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## This note was uploaded on 10/03/2011 for the course PHYS 212 taught by Professor Tedeschi during the Spring '08 term at South Carolina.

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18 - Fields from Currents - PHYS 212 Fall 2009 Fields Due...

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