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-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.

Part A:

What emf is induced in the coil if the subject shifts his gaze by 5 in 0.18 s ?

Explanation / Answer

Emf induced = - N*d/dt
Where = B.A*[Cos(final) - cos(intital)]

B = 1.5 T
A = *(3.0 * 10^-3)^2 = 2.83 * 10^-5 m^2
N = 18
Substituing Values,
e = - N*d(B.A*[Cos(95) - cos(90)]) /dt
e = - (18 * 1.5*2.83 * 10^-5)/0.18 * (-0.087) V
e = 3.69 * 10^-4 V
Induced emf in the coil, e = 3.69 * 10^-4 V

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