Transcranial magnetic stimulation (TMS) is a noninvasive technique used to stimu

Question

Transcranial magnetic stimulation (TMS) is a noninvasive technique used to stimulate regions of the human brain. A small coil is placed on the scalp, and a brief burst of current in the coil produces a rapidly changing magnetic field inside the brain. The induced emf can be sufficient to stimulate neuronal activity. One such device generates a magnetic field within the brain that rises from zero to 1.8 T in 100 ms. Determine the magnitude of the induced emf within a circle of tissue of radius 1.6 mm and that is perpendicular to the direction of the field.

Explanation / Answer

Induced emf, e = rate of change of magnetic flux

e = d(BA)/dt = A dB/dt

A = pi r^2 = pi (1.6 x 10^-3)^2 =8.04 x 10^-6 m^2

dB/dt = (1.8 - 0 ) / (100 x 10^-3) = 18 T/s

e = 8.04 x 10^-6 x 18 = 1.45 x 10^-4 volt

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