Question

Two very long, straight, parallel wires carry steady currents $I$ and $-I$ respectively. The distance between the wires is $d$. At a certain instant of time, a point charge $q$ is at a point equidistant from the two wires, in the plane of the wires. Its instantaneous velocity $v$ perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is

• A. $\frac{\mu_{0} I q v}{2 \pi d}$
• B. $\frac{\mu_{0} I q v}{\pi d}$
• C. $\frac{2 \mu_{0} I q v}{\pi d}$
• D. $0$

Answer 1

Answer: (D)

$0$

Answer 2

Net magnetic field due to the wires will be downward as shown in figure.
Since angle $v \square$ and $\vec{B}$ is $180^{\circ}$.
Therefore, magnetic force, $\vec{F}=q(\vec{V} \times \vec{B})=0$