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 (see figure). In TMS, 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 stimulate neuronal activity. (a) One such device generates an upward magnetic field within the brain that rises from zero to 1.50 T in 135 ms. Determine the induced emf around a horizontal circle of tissue of radius 2.00 mm. magnitude direction (b) The field next changes to 0.500 T downward in 95.0 ms. How does the emf induced in this process compare with that in part (a)? magnitude direction

Explanation / Answer

(A) induced emf = rate of change of magnetic flux

= d ( N BA )/dt

= N A dB/dt

= pi (1 x 10^-3)^2 (1.50) / (135 x 10^-3)

= 34.9 x 10^-6 V

= 34.9 uV ..........Ans

clockwise

(B) e = pi (1 x 10^-3)^2 (1.5 + 0.5) / (95 x 10^-3)

e = 66.1 x 10^-6 Volt

e = 66.1 uV .....Ans

counter clockwise

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