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Resistivity and Play-Doh

Voltmeters and Ammeters

Ammeter connected in circuit. 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.

Voltmeter connected in circuit. 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

[Can of Play-Doh]
From the Play-Doh Page of Wonders
  • Review of circuit used for experiment
  • Dependence on length? Demonstration using Play-Doh
    • Results: Graph
    • Conclusion: Resistance is directly proportional 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 inversely proportional to the cross-sectional area of a cylindrical resistor.
  • The Result!

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Comments, suggestions, or requests to ghw@udel.edu.

"http://www.physics.udel.edu/~watson/scen103/98w/clas0112a.html"
Last updated Jan. 9, 1998.
Copyright George Watson, Univ. of Delaware, 1996.