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Chapter 20: Electric Circuits
Example Problems
=
R
=
RSeries
ρL
A
=
I
1
∆V
R
2
=
PR IR ∆=
VR I=
RR
1
ΣR= Σ=
V
n
RParallel
Rn
n
Rn
R series
∆VR2
R
ΣVn 0
V=
S
Example 20.1
a. A 1.0-mm-diameter, 20-cm-long copper wire carries a 3.0 A current. What is the
potential difference between the ends of the wire? Hint: ρCu = 1.7 × 10−8 Ω∙m
b. A motorcyclist is making an electric vest that, when connected to the motorcycle's 12
V battery, will warm her on cold rides. She is using 0.25-mm-diameter copper wire,
and she wants a current of 4.0 A in the wire. What length wire must she use?
Example 20.2
The power rating of a light bulb is the power it dissipates when connected across a 120V potential difference. What is the resistance of (a) a 100-W and 60-W bulb? (b) How
much current does each bulb draw in normal use? (c) Car headlights are either a low or
high beam, is there more or less resistance in the high-beam filament?
Example 20.3
Determine the equivalent resistance of (a) circuit-1
and (b) circuit-2.
Example 20.4
For each circuit, compute the (a) equivalent resistance and (b) current through each
resistor.
Circuit 1
Circuit 2
Example 20.5
For a circuit shown, find the current through and the voltage across
each resistor.
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