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

Question

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 0.022 m2 and a normal that is parallel to a magnetic field of 1.0 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.

Explanation / Answer

Note that for constant area,

emf = A (Bf - Bi)/t

--> t = emf/[A(Bf - Bi)]

where

A = area
Bf = final value of B = 0 T
Bi = initial value of B = 1.0 T
emf = the induced voltage
t = time

thus,

t = 0.4545 s   [ANSWER]

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