Motion of an electron in a Magentic Field

[Wiseman101]

Homework Statement

Plot the motion of an electron in the x-y plane due to a magnetic field in the z plane. The initial position is at the origin. The initial velocity can be chosen at will.

Homework Equations

F = q(vXB)

The Attempt at a Solution

The program I am using is Matlab. I tried plotting the motion using the following set of equations, but the motion was a spiral, not circular. Any pointers in the right direction would be much appreciated!
(Vx is the velocity in the x direction, x is the position, etc..)

w=q/m

Vx(i+1) = Vx(i) + w*(Vy(i)*B)*dt
x(i+1) = x(i) + Vx(i)*dt

Vy(i+1) = Vy(i) + w*( -Vx(i)*B)*dt
y(i+1) = y(i) + Vy(i)*dt

 

[ideasrule]

It's probably spiral in MATLAB because of integration errors. It seems you think that the motion has to be circular because a magnetic field always applies a force perpendicular to the electron's motion, and you'd be right.

 

[Wiseman101]

Well as long as my equations are right then that's ok