Question

a proton, moving east, enters a magnetic field of a certain strength. because of this field the proton curves downward. what is the direction of the magnetic field?

Answer 1

F = q V X B

Using the right hand rule (right hand screw) turn V into B to get direction of force which in this case is down

If V is east and F is down then one can see that B must be directed towards the south - turn V into B (south) and F will be directed downwards.