Answer
(a) The initial force on the particle is directed upward.
(b) The initial force on the particle is directed to the left.
Work Step by Step
We can write an expression for the force on the particle:
$F = q~(v\times B)$
(a) By the right hand rule, the initial force on the particle is directed upward.
(b) By the right hand rule, if the particle were positively charged, the initial force on the particle would be directed to the right. Since the particle is negatively charged, the initial force on the particle is directed to the left.
