Question

 A long straight wire carries a current. The strength of the magnetic field, due to the wire, 10.0 cm from the axis of the wire is 20T . Determine the current in the wire. 

Answer 1

$I=\frac{2\pi Br}{\mu_0}=\frac{2\pi\cdot 20\cdot10^{-6}\cdot0.1}{4\pi\cdot 10^{-7}}=10~A.$