Resistance and Resistivity (Play-Doh™ Lab) – PHY 142/162
Introduction & Background: Include at least the following.
 Goals: Measure resistance R and resistivity  for an object made of Play-Doh.
See whether R or  are constant as the length of the object varies. Test different
samples of the material.
 Background: Define R and , show how they are related, explain how they are
measured in this lab. Include relevant equations and explain what the symbols
mean. Do you expect either R or  to be constant, and why?
Data: One table for each sample, and a summary table.
Analysis: For each sample, quote relevant quantities and answer these questions.
1) Is R constant? Compare % Var(R) vs. %Unc
2) Is  constant? Compare %Var() vs. %Unc
Conclusions
1) For each sample, provide ± ,
with ave and  = ax(%Unc, %Var())/100.
2) What more can you say about the entire set of samples you tested?
Additional Questions
In the following, all wires are made of the same material; and there is only one battery,
which (ideally) delivers a constant voltage between its leads. For all answers, explain
your reasoning.
1. A piece of wire is connected to a battery. If the wire is heated, its resistivity increases.
Indicate how this will affect the following quantities: the resistance of the wire, the
voltage drop across the wire, and the current through the wire.
2. A piece of wire is connected to a battery. This is replaced by a second piece of wire,
twice as long as the first one. Indicate how each of the following quantities is affected:
the resistivity, the resistance, the voltage drop across the wire, and the current through
the wire.
3. A piece of wire is connected to a battery. This is replaced by a second piece of wire,
with twice the diameter of the first piece. Indicate how each of the following quantities
is affected: the resistivity, the resistance, the voltage drop across the wire, and the
current through the wire.