An optical fiber made of glass with an index of refraction 1.50 that is coated with a material with index of refraction 1.30 has a critical angle of

A critical angle of 60.1°

Explanation:

Let's say

n1 Refractive index of rarer medium

n2 Refractive index of denser medium

So using the relation

စc= Sin^ -1(n1/n2)

So

စc = Sin^-1(1.3/1.5) = 60.1°

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answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.