F = qv x B = qvB sin(O). q is the electrons charge = 1.6x10-19 C. v is the electrons speed = 2x105 ms-1 . B is the magnetic field strength = 0.5 T. O is the angle between the electrons velocity vector and the magnetic field vector. Velocity is perpendicular to field so O = 90 degrees, sin(90)=1 therefore: F=qvB. Plugging the values into the equation we have :F= 1.6x10-19 x 2x105 x 0.5 Cms-1 T Therefore F=1.6x10-14 N