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 1.4 T in 100 ms.  Determine the induced emf within a circle of tissue of radius 1.2 mm and that is perpendicular to the direction of the field.

Explanation / Answer

solution:

Given, B = 1.4T, dt = 100ms = 100*10^-3s

dB = (1.4T - 0) = 1.4T

r = 1.2mm = 1.2*10^-3 m

induced emf is given by

induced emf = dPhi / dt = ((dB)*A*Cos theta) / dt

= ((1.4T - 0)*(pi*(1.2*10^-3 m)^2)* cos 0) / (100*10^-3 s)

= 0.633*10^-4 V

= 0.0633 mV

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