magnetic forces

Question

An electron travels with a speed of 2.60 x 106 m/s in a magnetic field of 0.30 T. What is the magnitude of the force exerted on the electron?

Answer 1

The question must say" the electron is moving perpendicular to magnetic field" . Then only the given answer will be correct.

Answer 2

To answer this question correctly, we need to know the angle θ between the velocity vector v of the electron, and the magnetic field B.  Then we can compute

 

F = qv x B = -ev x B

 

If v and B are perpendicular, we can compute the magnitude of the force as

 

F = qvB sinθ = evB sin90º = evB(1) = (1.6 x 10^-19 C)(2.60 x 10⁶ m/s)(0.30 T) = 1.248 x 10^-13 N

 

Is there a different angle θ missing from the problem statement?