Magnetic resonance imaging (MRI) is a medical technique forproducing \"pictures\

Question

Magnetic resonance imaging (MRI) is a medical technique forproducing "pictures" of the interior of the body. The patient isplaced within a strong magnetic field. One safety concern is whatwould happen to the positively and negatively charged particles inthe body fluids if an equipment failure caused the magnetic fieldto be shut off suddenly. An induced emf could cause these particlesto flow, producing an electric current within the body. Suppose thelargest surface of the body through which flux passes has an areaof 0.041 m2 and a normal that is parallel to a magneticfield of 2.0 T. Determine the smallest time period during which thefield can be allowed to vanish if the magnitude of the averageinduced emf is to be kept less than 0.011 V.

Explanation / Answer

given induced emf = 0.011V area of body surface exposed A = 0.041m2 magnetic field B = 2.0T initially when the field is on , the flux through the bodyis    i = BAcos00        =(2.0T)(0.041m2)         = 0.082Wb the induced emf in the body is     = -d/dt        =-[0-0.082/t] or t = 0.082Wb / 0.011V            =---------------        =(2.0T)(0.041m2)         = 0.082Wb the induced emf in the body is     = -d/dt        =-[0-0.082/t] or t = 0.082Wb / 0.011V            =---------------

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