Answer:
[tex]B= 7.5*10^{-15}T[/tex]
Explanation:
The magnetic field strenght on the z-axis at a distance d from the center is,
[tex]B= \frac{\mu_0 Q\omega R^2}{8\pi d^3}[/tex]
Our values are:
[tex]R=20cm\\Q=30mc\\w=5rad/s\\d=2*10^3cm=20m[/tex]
Replacing,
[tex]B= \frac{(4\pi*10^{}-7)(30*10^{-3})(5)(0.2)^2}{8\pi(20)}[/tex]
[tex]B= 7.5*10^{-15}T[/tex]