Experiments to study vision often need to track the movements of a subject\'s ey

Question

Experiments to study vision often need to track the movements of a subject's eye. One way of doing so is to have the subject sit in a magnetic field while wearing special contact lenses with a coil of very fine wire circling the edge. A current is induced in the coil each time the subject rotates his eye. Consider the experiment shown in the figure in which a 18-tum, 6.0-mm-diameter coil of wire circles the subject's cornea while a 1.5 T magnetic What emf is induced in the coil if the subject shifts his gaze by 4 degree in 0.25 s ? Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

formula for induced emf is

e= - dflux/ dt

initial flux = N BA cos theta = 18*1.5 pi ( 3* 10^-3 )^2 cos 0 = 0.00076302 T m^2

final flux =  N BA cos theta = 18*1.5 pi ( 3* 10^-3 )^2 cos (90-4) = 5.322* 10^-5 T m^2

e= ( final flux- initial flix)/dt

=  5.322* 10^-5-0.00076302 T m^2/0.25 s

=2.83 mV

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