Magnetic field of lightning?

Question

The return stroke of a bolt of lightning typically carries a peak current of 19 kA up from the ground. What is the maximum magnetic field associated with the bolt 0.5 m away?

Answer 1

The magnetic field from a line current is given by

B = µ0*I/(2*π*r); put in r = .5m, I = 19*10^3A and µ0 = 4*π*10^-7 tesla*m/amp