Two very long straight parallel wires carry currents i and 2 i in opposite directions. The distance between the wires is r . 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 is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is

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Let the two wires be placed along the y -axis at x = -r/2 and x = r/2 . The wire at x = -r/2 carries current i in the +y direction, and the wire at x = r/2 carries current 2i in the -y direction. The point charge q is at the origin (0,0,0) and its velocity is v = v k . The magnetic field B ₁ due to the first wire at the origin is given by the right-hand rule. The distance is r/2 . The field is B ₁ = ₀ i 2 (r/2) k = ₀ i r k . The magnetic field B ₂ due to the second wire at the origin. The current is 2i in the -y di