Magnetic resonance imaging (MRI) is a medical technique for producing pictures i

Question

Magnetic resonance imaging (MRI) is a medical technique for producing pictures inside a human body. The patient is placed within a strong magnetic field. One safety concern involves possibly exposing a patient to sudden spikes in voltage should power fail and the field turn off. Suppose the exposed surface body would 0.032 m^2 perpendicular to a field of strength 1.5 T. What is the quickest time period during which the field could drop to zero if the average induced emf has to be kept less than 0.010 V.

Explanation / Answer

Given A = 0.032 m^2

initial is 1.5 T

final is 0

so change in magnetic field dB = 1.5 T

emf e = 0.01 V

induced emf e = d(B* A * cos(theta)) / dt

e = A * dB / dt

0.01 = 0.032 * 1.5 / dt

time required = 4.8 s

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