Question

Magnetoencephalography (MEG) is a technique for measuring changes in the magnetic field of the brain caused by external stimuli such as touching the body or viewing images of food. Such a change in the field occurs due to electrical activity (current) in the brain. During the process, magnetic sensors are placed on the skin to measure the magnetic field at that location. Typical field strengths are a few femtoteslas (1 femtotesla = 1 fT = 10

Answer 1

Since the sensor is on the axis of the circular loop (one hemisphere), we would use the formula

Here B_Z= 5.15 * 10^-15 T, , R= 65/2 = 32.5 mm= 32.5 * 10^-3 m, z= 2.7 cm= 0.027 m.

Putting the values we get,

5.15 * 10^-15 = 4 * 10^-7 * 2 * * (0.0325)² / 4 * [(0.027)² + (0.0325)²]^3/2.  

= 5.85 * 10^-4 A

To determine the magnetic field at the centre of the loop (hemisphere)-

So, putting the values we get

B= 4 * 10^-7 * 5.85 * 10^-4 / 2 * 0.0325 = 73.476 * 10^-11 / 0.065 =1.13 * 10^-8 T.