Magnetic field question

Question

The magnetic field 40.0 cm away from a long, straight wire carrying current 2.00 A is 1.00 μT.

(a) At what distance is it 0.100 μT?

(b) at one instant, the two conductors in a long household extension cord carry equal 2.00 A in opposite directions. The two wires are 3.00 mm apart. Find the magnetic field 40.0 cm away from the middle of the straight cord, in the plane of the two wires.

Answer 1

B= µ_oI/2π/r= magnetic field strength and µ_o= 4πE-7 T-m/ampere thus B = 2*2/rE-7 = 2E-6 at =0.2m a)

b) B= 2*2E-7*2/.0015= 533 μT