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20.  Magnetic
resonance imaging (MRI) is a medical technique for producing pictures of the
interior of the body. The patient is placed within a
strong magnetic field. One safety concern is what would happen to the
positively and negatively charged particles in the body fluids if an
equipment failure caused the magnetic field to be shut off
suddenly. An induced emf could cause these particles to flow, producing an
electric current within the body. Suppose the largest surface of the body
through which flux passes has an area of 0.032 m2 and a normal that is parallel
to a magnetic field of 1.5 T. Determine the smallest time period during which
the field can be allowed to vanish if the magnitude of the average induced
emf is to be kept less than 0.010 V.
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