Chapter 28, Problem 005 An electron moves through a uniform magnetic field given by B B + 2.20 At a particular instan, the electron has e ocity V 1.83 ·45 m sandthe magnetic for e acting t , as?r 9 Number Units the tolerance is +/-390 Solution We know that F = q ( v x B) F Z = q ( v x B y - v y B x ) k F Z = q( v x ( 2.20 B x ) - v y B x ) k F Z = q ( 2.20 v x - v y ) B x B x = F Z / q (2.20 v x - v y ) where v x = 1.83 m/s v y = 4.45 m/s and   q = -1.6 x 10^-19 C B x = 2.18 x 10 -19 N / ( -1.6 x 10 -19 C)  [ (2.20 ) ( 1.83 m/s) - (4.45 m/s ) ] B x = -0.236 T .