Question

7) Why does total internal reflection happen? Why can't fiber optic cables be bent beyond 90 degrees?

Answer 1

when a light passes from a medium of one refractive index to another medium with a lower refractive index it bends or refracts away from the line perpendicular to the surface.

at a perticular angle light canot go to the another medium

such an angle is called as critical angle

from snells law

sin(crtical angle) = n2/n1

the critical angle is the angle of incident ray which causes the refracted ray to bend the angle of 90 degrees. there fore any angle of incidence beyond the critical angle means that the light ray is going to bend inwards. this is the internal reflection.