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 17-turn, 6.0-mm-diameter coil of wire circles the subject's cornea while a 1.2T magnetic field is directed as shown. The subject begins by looking straight ahead.

What emf is induced in the coil if the subject shifts his gaze by 4? in 0.16s ?

Explanation / Answer

Initial magnetic flux through the coil is :

.

A = area of coil = ?*d*d/4

.

?1 = N*B*A*cos?

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= 17*1.2*(?*0.006*0.006/4)*cos0`

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= 5.77*10-4 Tm2

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Final flux after 0.16 s is :

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?2 = N*B*A*cos?

.

= 17*1.2*(?*0.006*0.006/4)*cos4`

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= 5.754*10-4 Tm2

.

So, change in flux

.

= ?2-?1

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= -1.6*10-6 Tm2

.

So, Rate of change of flux

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= [?2-?1]/0.16 Tm2/s

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= -1.0*10-5 Tm2/s

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Now, emf induced = -??/?t =[?1-?2]/0.16 V = 1.0*10-5 V

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