Rheostat, a device used to regulate an electric current by increasing or decreasing the resistance of the circuit. Some common uses of the rheostat are to dim lights, to control the speed of an electric motor, and to control the volume of a radio. The accompanying diagram shows a simple rheostat. Current flows into the resistance coil and from the resistance coil through the slider. When the control knob is turned, the slider moves along the coil; the amount of resistance is thus changed by varying the length of the current's path through the resistance coil.
We first reported on the possibility of an invisibility cloak last year. Now a different invisibility cloak is making the news -- one that uses metamaterials to redirect light away from the wearer.
Uranium -- the stuff of futuristic energy and atomic weapons. Mining for this valuable element is anything but dull. Think you know how uranium mining works? Take this quiz to find out.