Question

A vertical wire carries a current in upward directon. If an electron beam sent horizontally towards the wire, then it will deflected

• A. Vertically downwards and perpendicular to the plane of the paper
• B. Vertically upwards and perpendicular to the plane of the paper
• C. In the plane of the paper
• D. No deflection

Answer 1

Answer: (B)

$\overset{ \rightarrow }{F}=q\overset{ \rightarrow }{V}\times \overset{ \rightarrow }{B}$
$=-eV\hat{i}\times B\left(- \hat{j}\right)$
$\overset{ \rightarrow }{F}=eVB\hat{k}$
Force is vertically upwards perpendicular to plane of paper.