Prelim Question (1 Viewer)

I97

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"The critical angle for a new underwater optical fibre material is found to be 64 degrees. If the refractive index of water is 1.33, calculate the refractive index of the test material." The answer is 1.48 i just can't get there.
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Axio

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sin i / sin r = n2/n1, i=64, r=90, n2=1.33, n1=?

sin64/sin90=1.33 / n1
sin90/sin64= n1 / 1.33
sin90 x 1.33 / sin64 = n1 = 1.48
 

Axio

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Note: because the water is the outer part of the fibre (I think), the water had to be less dense than the test material i.e. have a lower refractive index and therefore be equal to n2.
 

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