Question

A negative test charge is moving near a long straight wire carrying a current. The force acting on the test charge is parallel to the direction of the current. The motion of the charge is:

• A. Away from the wire
• B. Towards the wire
• C. Parallel to the wire along the current
• D. Parallel to the wire opposite to the current

Answer 1

Answer: (B)

Force on a moving charge, $\overset{ \rightarrow }{F}=q\left(\overset{ \rightarrow }{v} \times \overset{ \rightarrow }{B}\right)$
Here, $\because q=-ve \, $
$\Rightarrow \overset{ \rightarrow }{F}=-q\left(\overset{ \rightarrow }{v} \times \overset{ \rightarrow }{B}\right)$
$\therefore \text{motion of}-q\text{ is towards the wire.}$