The large magnetic fields used in MRI can produce forces on electric currents wi

Question

The large magnetic fields used in MRI can produce forces on electric currents within the human body. This effect has been proposed as a possible method for imaging "biocurrents" flowing in the body, such as the current that flows in individual nerves. For a magnetic-field strength of 12 T , estimate the magnitude of the maximum force on a 1-mm-long segment of a single cylindrical nerve with a diameter of 1.5 mm. Assume that the entire nerve carries a current due to an applied voltage of 120 mV (that of a typical action potential). The resistivity of the nerve is 0.6 ??m.

Express your answer in newtons to one significant figure.

Explanation / Answer

rho = 0.6 ohm m

R = rho L / A = (0.6) (1 x 10^-3) / ( pi (1.5 x 10^-3 / 2)^2)

R = 339.5 Ohm

I = V / R = 3.53 x 10^-4 A

F_max= IL B = (3.53 x 10^-4) (1 x 10^-3)(12)

F_max = 4 x 10^-6 N ....Ans

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