Question

a long wire carries a current toward the north in a magnetic field that is directed vertically downward. what is the direction of the force on the wire?

Answer 1

F = Q v B where Q is negative (electron motion)

v will be directed from Plus to Minus (conventional current)

F = Q (v X B) vector notation

v will be positive in northerly direction (plus charges in direction of current)

v X B will be directed towards the "West"

Since Q lis negative the net force is directed to the "East"

As a check one can use the "Left Hand Rule":

First finger in direction of field "Down"

Second finger in direction of positive charges "North"

Thumb (force) will be west and since the charge is negative the net force is towards the "East"