Alight beam has speed c in vacuum and speed v in a certain plastic. the index of refraction n of this plastic isn=cvn=(v/c)^2n=v/cn=c/vn=(c/v)^2

Explanation:

The index of refraction of a material is defined as:

where

c is the speed of light in vacuum

v is the speed of light in the material

The speed of light in the material, v, is always smaller than the speed of light in vacuum, c: therefore, this ratio is always greater than 1. The index of refraction basically tells how much is the light slowed down in a material: the greater the value of the index of refraction, the slower light travels in that medium.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it

i would say