What is total internal reflection? when does it occur?

Total internal reflection is the phenomenon that occurs when a ray of light travels from a medium of high refractive index to a lower refractive index medium.

In this sense, the ray is refracted in such a way that it is not able to cross the surface between both media, being completely reflected.

This is the physical principle used in optical fiber to conduct light through the fiber without energy loss.

It is important to note, that this phenomenon occurs at a limit angle , which is calculated from Snell's law, substituting the angle of the second medium by :

Where and are the refractive indexes of both media.

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