Typical field strengths are a few femoteslas (1fT=10^-15T). An adult brain is about 140mm wide, divided into two sections (called hemispheres) each about 70mm wide. We can model the current in one hemisphere as a circular loop, 65mm in diameter, just inside the brain. The sensor is placed so that it is along the axis of the loop 2.30cm from the center. A reasonable magnetic field is 4.35fT at the sensor. According to this model, what is the current in the brain?
What is the magnetic field at the center of the hemisphere of the brain?