Q81 / 90 · JEE Main 2017 (09 Apr Online) · Physics

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
Correct answer
B
Towards the wire
C
Parallel to the wire along the current
D
Parallel to the wire opposite to the current

Solution

Force on a moving charge, $\vec{F} = q (\vec{v} \times \vec{B})$

Here, $∵ q = - v e$

$\Rightarrow \vec{F} = - q (\vec{v} \times \vec{B})$

$∴ motion of - q is towards the wire.$

Hence, the correct answer is option: 'B'.

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