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.
Total Internal Reflection and the Critical Angle. If a ray of light is leaving a denser medium, it will bend away from the normal. As can be seen from the above diagram, as the angle of incidence inside the material increases the angle of refraction increases to a point at which it leaves the material at 90Ë.
The law of reflection says that when a ray of light hits a surface, it bounces in a certain way, like a tennis ball thrown against a wall. The incoming angle, called the angle of incidence, is always equal to the angle leaving the surface, or the angle of reflection. When light hits a surface at a low angle -- like on a lake at sunset -- it bounces off at the same low angle and hits your eyes full blast, rather than obliquely as when the sun sits overhead.