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Discussion Question 6B
P212, Week 6
Kirchoff’s Law Analysis of a Resistor Network
So we now have two methods for analyzing resistor networks.
Which one should we use?
(i) It depends on the particular problem, and
(ii) often a
mixture
of methods is the best.
In general, method 1 (successive combination of elements) is easier, but method 2 (Kirchoff’s Laws) is
more powerful .
.. and some circuits simply
cannot
be analyzed with method 1 alone.
The circuit shown at right is a typical example:
here
we have
three
batteries and they prevent us from
“collapsing”
any
of the resistors in groups, as none of
them are in simple series or parallel combinations.
Our only chance is to use Kirchoff’s Laws!
Let all the resistors R
i
have resistance 10
Ω
, and let the
battery EMF’s be
E
1
= 10 V,
E
2
= 20 V,
E
3
= 30 V.
Your tasks are:
(a)
Find the
current I
3
through resistor R3.
(b) Find the electric
potential difference, V
A
V
B
, for
the points A and B indicated on the
circuit.
5
Looking at the right most branch, we see
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This note was uploaded on 06/16/2011 for the course PHYS 212 taught by Professor Kim during the Spring '08 term at University of Illinois, Urbana Champaign.
 Spring '08
 Kim
 Magnetism, Work

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