MasteringPhysics Tutorials, Chapter 21
MasteringPhysics tutorials assume that you have the formula in front of you. Open your
book to the Chapter Summary on page 751. Many questions can usually be answered by
examining or using the formula.
Resistance and Resistivity
Use both
R=V/I
and
R =
ρ
L/A
. List all of the physical quantities (letter symbols) in these
two formulas. The given conditions are that both wires have the same voltage applied,
V
,
so that can’t be different and both are made of the same material (copper) so their
resistivities,
ρ
, can’t be different. Thus, the other quantities may be different.
Dependence of Resistance on Resistor Dimensions Ranking Task
Use
R =
ρ
L/A
. You are not given
ρ
but you are give
L
and can calculate
A
. For example,
imagine current is traveling along the x axis and enters the 4 cm by 10 cm face of the
block. It will travel through 3 cm of the material. So, call the resistance along the x axis
Rx
. Then,
3cm
3
4cm
10cm
40cm
L
Rx
A
ρ
ρ
ρ
⎛
⎞
⎛
=
=
=
⎜
⎟
⎜
×
⎝
⎠
⎝
⎞
⎟
⎠
Now, do the same computation for
Ry
and
Rz
and rank the three answers.
Kirchhoff's Loop Rule Conceptual Question
You just had a lab exercise on “Measuring Voltage”. Recall what you learned there about
voltage.
Kirchhoff's Current Rule Ranking Task
Imagine the wires in the circuit to be pipes. Current is the same as water flowing through
the pipes.
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 Spring '10
 Bratton
 Resistance, Resistor, Series and parallel circuits, voltage divider rule, equivalent resistance, Kirchhoff

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