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Unformatted text preview: ECE312 Autumn 2010: Problem Set 1 Solutions Problem 1 : B = 5 y T, u = 3 x + 4 z m/s, m e = 9 . 1 10 31 kg, and q e = 1 . 6 10 19 C. (a) The force on the electron: F = q u B = ( 1 . 6 10 19 )(3 x + 4 z ) 5 y = 5( 1 . 6 10 19 )(4 10 7 )(3 z 4 x ) = (5 . 03 10 24 )(0 . 8 x . 6 z ) N (b) The radius of the circular orbit: vextendsingle vextendsingle F vextendsingle vextendsingle = 5 . 03 10 24 = m  u  2 r r = (9 . 1 10 31 )(5) 2 (5 . 03 10 24 ) = 4 . 52 m (c) Given a circular orbit, the distance traveled in one orbit is 2 r . Since the velocity  u  is 5 m/s, the time required to complete one orbit is 2 r  u  = 5 . 68 s f = (5 . 68 10 6 ) 1 = 175 . 94 kHz This is called the gyrofrequency of the electron. Electrons circulating in these sorts of orbits are often used in devices for studying particle physics. Problem 2 : A coaxial cable with J = z (1+ r 2 ) flowing through a solid inner cylinder of radius 2 cm. The current returns on the outer shell of radius 5 cm. (a) Note this is a nonuniform current density, i.e. the current is less in the middle of the wire than on the outside following the function (1+ r 2 ). To use Amperes Law to find fields, we need a lot of symmetry. Here we have a cylindrical structure, so we choose a cylindrical coordinate system for this problem. In general the field would look like H ( r, , z ) = rH r ( r, , z ) + H ( r, , z...
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This note was uploaded on 01/11/2012 for the course ECE 312 taught by Professor Johnson,j during the Fall '08 term at Ohio State.
 Fall '08
 Johnson,J
 Electromagnet

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