Phys 259, Labatorial 7, Winter 2017
University of Calgary
Department of Physics and Astronomy
PHYS 259, Winter 2017
Labatorial 7: Electrical Resistivity of Play-Doh
TM
One of the most basic circuit elements is a resistor,
which is a device that dissipates energy. Resistive de-
vices come in all shapes and sizes as can be seen in the
photo on the right, which is not surprising because
there is a connection between a device’s resistance
and its geometry. The two are related by an intrinsic
property of the material itself called the
resistivity
.
For instance, any two pieces of copper will have the
same resistivity but their individual resistances will
depend on their shapes.
In this labatorial, you will
explore this connection between geometry and resis-
tance by using objects made of Play-Doh
TM
as resis-
tors in a circuit.
Learning Goals:
To understand how the resistance of an object depends on its geometric properties.
Preparation:
Halliday, Resnick, and Walker, “Fundamentals of Physics” 10th edition, Wiley: 26.1–26.5
Equipment:
Anatek power supply, digital multimeter, 3 banana plug connecting cables, 2 alligator clips, 2 aluminum
plates, 2 voltage probes, Play-Doh
TM
, ruler, computer with LoggerPro software.
Note that there is an equation sheet at the end of this worksheet.
1

Phys 259, Labatorial 7, Winter 2017
1
Resistance is a Geometrical Property
Every material has an intrinsic property known as the resistivity
ρ
. Objects made out of a material have a
property called the resistance
R
that depends on the object’s geometry. The relationship between resistance
and resistivity is
R
=
ρL
A
(1)
where
L
is the length of the object and
A
is its cross-sectional area perpendicular to its length. Consider a
solid metal cylinder of length
L
and radius
r
. You measure the resistance of this cylinder and find it to have
a value
R
.
Question 1
: If you cut the cylinder in half so that you had two pieces each of length
L/
2, as shown in the
diagram, what would be the resistance of each piece according to Eq. (1)?
in series? Explain.
Question 4
: If you took the two pieces arranged side-by-side as shown and considered them a single object
of length
L/

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