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. Parallel to the wire along the current
• C. Towards the wire
• D. Parallel to the wire opposite to the current

Answer 1

Answer: (C)

Towards the wire

Magnetic field at A $\to$ out of the plane of the paper

$B=B_0\hat{k}$

$\Rightarrow$ force on charged particle:

$\Rightarrow F=-q\overrightarrow{v}\times \overrightarrow{B}$

$\Rightarrow F=+qv{B}_0\hat{j}$

Therefore, the particle moves towards the wire.