I just want to check my reasoning. We have a particle starting at the origin with
There is a magnetic field pointing in the $\hat x$ direction and an electric field pointing in the $\hat z$ direction. What happens right after $t=0$?
I think one of these 3 things will happen:
If the magnetic field affects the particle first, then it will initially start to curve downwards.
If the E-field affects the particle first, then it will initially curve upwards.
If both fields affect the particle initially, then I think the particle will move in a straight line from the origin along the $y$-axis.