# SCEN103 Class 13

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### Resistivity and Play-Doh

#### Voltmeters and Ammeters

 An ammeter measures current through a circuit element; -- therefore it must be connected in series with it. An ammeter should have a much lower resistance than the other elements in the circuit; -- otherwise current may change significantly. Consider effective resistance. A voltmeter measures voltage across a circuit element; -- therefore it must be connected in parallel with it. A voltmeter should have a much higher resistance than the element in parallel; -- otherwise voltage will change significantly. Again, consider effective resistance.

#### Resistance of a cylinder

• Review of circuit used for experiment
• Dependence on length? Demonstration using Play-Doh
• Results: Graph
• Conclusion: Resistance is ??? to the length of a cylindrical resistor.
• Dependence on diameter? Group Activity
• Procedure
• Data: collected by groups from previous term
• Graph: R vs. Diameter
• Graph: R vs. Reciprocal Diameter
• Graph: R vs. Reciprocal Area
• Conclusion: Resistance is ??? to the cross-sectional area of a cylindrical resistor.
• The Result!

Comments, suggestions, or requests to ghw@udel.edu.
"http://www.physics.udel.edu/~watson/scen103/99s/clas0310.html"
Last updated March 10, 1999.
Copyright George Watson, Univ. of Delaware, 1996.