The wire that carries the current from the power source to the outlet or receptacle is the hot wire. Whenever you see a black wire, you know it is hot. There are other wires that carry current in more complicated circuits, but black are always hot.
The minimum angle at which total internal reflection occurs is known as the critical angle (for Perspex this is about 43Ë). At any angle greater than the critical angle, total internal reflection occurs and the light ray obeys the normal rules for reflection (i.e. angle of incidence = angle of reflection). 1  Page. 2  1. 3  2.
1 The angle between this ray and the perpendicular or normal to the surface is the angle of incidence.  The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface. The angle between the surface normal and the reflected ray is known as the angle of reflection.