Center For Integrating Research and Learning

ArrowRheostat

This is a Java tutorial, which requires that you have Java, a free software, installed on your computer. It works best if you have the latest version of Java installed. If you are having trouble viewing or using this tutorial, try downloading the latest version of Java.

In the mid 1820s, Georg Ohm, a German professor of mathematics, began investigating electrical resistance. Through experimentation Ohm determined that all materials exhibit at least some resistance to electric flow, even the most conductive metals. He further found that when the conductive material was the same, a thin wire was more resistant to electricity than a thick one and a long wire was more resistant than a short one. Equipped with this knowledge, scientists were able to develop useful means of varying the resistance in a circuit, such as the rheostat, which was developed in the mid 1800s by Charles Wheatstone.

Most early rheostats, including the one depicted in this interactive tutorial (a successor to Wheatstone's original), consisted of numerous turns of resistance wire wound around an insulated tube above which a metal bar was positioned. A sliding contact connected the wire to the bar and could be moved to change the amount of coiled wire an electric current traveled through before it was passed on to the bar, which was less resistant to flow.



Interactive Java Tutorial
ATTENTION
Our servers have detected that your web browser does not have the Java Virtual Machine installed or it is not functioning properly. Please install this software in order to view our interactive Java tutorials. You may download the necessary software by clicking on the "Get It Now" button below.

 



To operate the tutorial, adjust the rheostat slider. This action moves the contact between the coil and the bar along the length of the tube, changing the resistance of the rheostat. An ammeter is included in the circuit to provide a means of gauging the strength of the current, which varies depending on the resistance of the rheostat. The resistance is lowest when the contact is placed at the far left of the coil, where the current is able to immediately flow through the bar rather than first passing through the much longer and narrower (and thus more electrically resistant) piece of wire composing the coil. Increased resistance occurs as the contact is moved to the right, so that the electricity must travel through an increasing amount of resistance wire coiled around the tube. The more resistance provided by the rheostat, the smaller the current that reaches the ammeter.

Related Electricity & Magnetism Pages


© 1995–2014 National High Magnetic Field Laboratory • 1800 E. Paul Dirac Drive, Tallahassee, FL 32310–3706 • Phone: (850) 644–0311 • Email: Webmaster

NSF and State of Florida logos NSF logo State of Florida logo


Site Map   |   Comments & Questions   |   Privacy Policy   |   Copyright   |   This site uses Google Analytics (Google Privacy Policy)
Funded by the National Science Foundation and the State of Florida