The figure shows three situations when an electron moves with velocity $\vec v$ travels through a uniform magnetic field $\vec B$. In each case, what is the direction of magnetic force on the electron
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$1.$ $\vec{F}_{m}=(-e)(-v \hat{i} \times B \hat{j})=-$Bev $\hat{k}$ i.e. $-z$ $-axis$
$2.$ $\vec{F}_{m}=(-e)(-v \hat{j} \times B \hat{k})=-$Bev$\hat{i}$ ie. $-x$ $-axis$
$3.$ $\vec{F}_{m}=(-e)(-v \hat{j} \times B \hat{k})=0$
Alternatively, use Fleming's left hand rule.
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