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.
Almost every object will reflect light in some way. In fact, if an object does not produce its own light it will not be visible if it does not reflect that of other sources. Reflection works by angles. Light shines onto a surface in what is called an incident ray. The angle that this ray strikes the surface of the object is measured by imagining a line coming out from the surface at the point that the light strikes it, at right angles to the object.