Patients undergoing an MRI occasionally report seeing flashes of light. Some pra

Question

Patients undergoing an MRI occasionally report seeing flashes of light. Some practitioners assume that this results from electric stimulation of the eye by the emf induced by the rapidly changing fields of an MRI solenoid. We can do a quick calculation to see if this is a reasonable assumption. The human eyeball has a diameter of approximately 25 mm. Rapid changes in current in an MRI solenoid can produce rapid changes in field, with Delta B/Delta t as large as 58 T/s What emf would this induce in a loop circling the eyeball? Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

Using Faraday's law of electromagnetic induction

induced emf is e = d(phi_B)/dt = A*(dB/dt) = pi*(d/2)^2*(dB/dt) = 3.142*(0.025/2)^2*58 =0.0284 V = 28.4 mV

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