Although the currents that cause this field are quite complicated, we can get a rough estimate of their size by modeling them as a single circular current loop 16 cm (the width of a typical head) in diameter. What current is needed to produce such a field at the center of the loop?

Incomplete question

Complete question:

The magnetic field of the brain has been measured to be approximately 3.0×10−12T. Although the currents that cause this field are quite complicated, we can get a rough estimate of their size by modeling them as a single circular current loop 16 cm (the width of a typical head) in diameter. What current is needed to produce such a field at the center of the loop?

I = current is 3.8 x 10^-7 A

Explanation:

Magnetic field at the center of the loop is given by, B= μI/2R but

I = 2RB/μ

given that B = 3x 10^-12 T

radius is 16cm which is 0.16 m /2 = 0.08m

we know that μ is 4π x 10^-7 T.A/m

Substituting the given values we get that

I= (2)(0.8m)(3x 10^-12 T))/ (4π x 10^-7T.A/m)

I = current is 3.8 x 10^-7 A

see earlier answer