In the figure above there are 4 wires that are perpendicular to the screen.
The current in the wires are +1 Amp, n1 Amp, n2 Amp, and +3 Amp.
The "+" direction is out of the screen. If the closed path
integral of B⋅dl = μ0 n3 where n3
is the number of Amps, what is n3.
Note that the direction of the path integral is clockwise.
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