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.
The female birth control pill has been around for decades, and many men would like to share the contraceptive responsibility. But despite the lingering promise of non-barrier, reversible male birth control options, the FDA has yet to approve any. As we wait for male birth control to become a reality, test your knowledge of its development so far.
Fusion reactors will use abundant sources of fuel, will not leak radiation above normal background levels, and will produce less radioactive waste than current fission reactors. Learn about this promising power source.