Question

A long straight horizontal wire carries a current = 3.90 A to the left. A positive 1.00 C charge moves to the right at a distance 1.50 m above the wire at constant speed v = 5000 m/s. What is the magnitude of the magnetic field at the location of the charge due to the current-carrying wire?

Answer 1

The field there will only depend upon the current in and distance from the wire. Use Ampere's law. You will find the formula at

http://www.pa.msu.edu/courses/1997spring/phy232/lectures/ampereslaw/wire.html