Magnetic fields

1. Nov 25, 2006

dcgirl16

an electron moves within a uniform magnetic field of .2T at a speed of 5x10^5 m/s. What is the magnetic force on the electron?

I used Fm=qvBSin and got 1.6x10^-14N but the answer is that it cant be determined with this info why not?

2. Nov 25, 2006

nrqed

Because you don't know the angle between the velocity of the electron and the magnetic field! You are right that the magnitude of the magnetic field is $F_m = |q| v B sin \theta$ but without the angle $\theta$ you can't find the answer. (how did {\em you} get an answer? I bet that you used an angle equal to 90 degrees!)

Patrick