The problem states:
Two long straight wires at separation d = 16.0 cm carry currents i1 = 3.61 mA and i2 = 3.00i1 out of the page.
(a) At what point on the x axis shown is the net magnetic field due to the currents equal to zero?
(b) If the two currents are doubled, is the point of zero magnetic field shifted toward wire 1, shifted toward wire2, or unchanged?
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d = 16.0 cm = 1.6 x 10-1 m
i1 = 3.61 mA = 3.61 x 10-3 A
i2 = 3.00i1 = 3.00(3.61 mA) = 10.83 mA = 1.083 x 10-2 A
L for each conductor is infinite
The right hand rule indicates both magnetic fields wrap to the left of both wires with the current coming out of the page. These two wires are parallel ...
I have shown how to find the location of zero magnetic filed between two parallel current carrying wires. I also have discussed the results as the current in the wire are doubled.