A long straight wire carries a current I = 10 A. At what distance is the magnetic field H = 1 A/m?

• A. 5/2π
• B. 10/2π
• C. 1/2 π
• D. 20/2π

Answer: (B)

The strength of a magnetic field is specified by the magnetic induction B or by the magnetic field strength H. A current I through a long, straight wire produces a magnetic field with strength H = I/2πr at a distance r from the wire.
Given
H = 1 A/m
I = 10 A
H = I/2πr
1 = 10/2πr
r = 10/2π