일반물리학 2 — Magnetic Fields Due to Currents: Problem 41

41 A surveyor is using a magnetic compass 12.2 m below a power line in which there is a steady current of 200 A. (a) What is the magnetic field at the site of the compass due to the power line? (b) Will this field interfere seriously with the compass reading? The horizontal component of Earth’s magnetic field at the site is 20 μT.