[quote author=Fu-Kwun Hwang link=topic=1972.msg7332#msg7332 date=1286248116]
What is the trajectory in your mind if there is an electron inside a vacuum with magnetic field?
[/quote]
a beam of electrons in helix?

[quote author=Fu-Kwun Hwang link=topic=1972.msg7332#msg7332 date=1286248116]
Assume the energy of the electron is 1keV: try to calculate it's velocity.
Assume the magnetic field is 1kG(Gauss)=0.1T(Tesla) and velocity is perpendicular to the magnetic field.
: try to calculate it radius and frequency.
[/quote]
0.5*m*v^2 = E
0.5*9.1*10-31*v^2 = 1*10^3*1.6*10^-19
v = 1.88*10^6 m/s

assume F = m*v^2/r is valid since perpendicular b and v
B*v*q = m*v^2/r
0.1*1.88*10^6*1.6*10^-19 = (9.1*10^-31*1.88*10^6)/r
r = 1.06x10^-4 m

assume circle path
2*pi*r / T = v
3.57x10^-10 s = T

[quote author=Fu-Kwun Hwang link=topic=1972.msg7332#msg7332 date=1286248116]
With the above calculated data: try to think of the motion of the electron.
[/quote]
a beam of electrons in helix moving away from the circular axes?

[quote author=Fu-Kwun Hwang link=topic=1972.msg7332#msg7332 date=1286248116]
If the velocity of the electron is not perpendicular: assume 1% of velocity is parallel to the magnetic field.
What do you think about the average motion of the electron will be look like?
[/quote]
look like a beam in the vz direction? a beam of electrons in helix motion moving away from the circular axes x and y?

Am i visualizing this.?
[img]http://www.mdahlem.net/img/astro/elgyro.jpg[/img]
http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?p=27760&sid=9a745d78c23d14d82acc194a8389c7a2

not sure whether this is what you mean  ;D