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 15-turn, 6.0-mm-diameter coil of wire circles the subject's cornea while a 1.5 T magnetic field is directed as shown. The subject begins by looking straight ahead. (Figure 1) What emf is induced in the coil if the subject shifts his gaze by 6 in 0.20 s ? Cornea. 6.0-mm-diameter coil Eye

Explanation / Answer

The flux in the coil is zero as shown, since the coil axis is perpendicular to the B-field, i.e. = 90°, Cos(90°) = 0

If the subject shifts his eye by 6°, the flux is B*A*Cos(84°)

= 1.2**(0.006/2)^2*Cos(84) = 3.55*10^-6 Tm^2

v = d/dt = /t = 3.55*10^-6/.2 = 1.775*10^-5 V = 1.8E-5 V

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