Answer:
Approximately [tex]143\; {\rm T}[/tex] assuming that this transmission line is straight and infinitely long.
Explanation:
Lookup the permeability of free space: [tex]\mu_{0} = 4\, \pi\; {\rm T \cdot m \cdot A^{-1}[/tex].
Consider an infinitely-long straight wire in empty space carrying a current of [tex]I[/tex]. At a distance of [tex]r[/tex] from this wire, the magnitude of the magnetic field from the wire would be:
[tex]\begin{aligned} B &= \frac{\mu_{0}\, I}{2\, \pi\, R}\end{aligned}[/tex].
In this question, it is given that [tex]I = 500\; {\rm A}[/tex]. At a distance of [tex]R = 7.0\; {\rm m}[/tex] from this wire, the magnitude of the magnetic field from this cable would be:
[tex]\begin{aligned} B &= \frac{\mu_{0}\, I}{2\, \pi\, R} \\ &= \frac{(4\, \pi \; {\rm T \cdot m \cdot A^{-1}}) \, (500\; {\rm A})}{(2\, \pi)\, (7.0\; {\rm m})} \\ &\approx 143\; {\rm T}\end{aligned}[/tex].
