Diana Wu
803576180
21 October, 2008
Physics 4BL Sec 5
DC and AC Circuits
II. Introduction
The purpose of this lab is to examine the properties and behaviors of DC and AC
circuits under given conditions. For DC circuits, we verify Ohm’s law, test out series and
parallel combinations, and examine the variation of the resistance of a length of copper
wire and that of a diode with temperature. For AC circuits, we combine series circuits
with reactive components and with resistors and study the results and we analyze RC and
RL circuits under transient conditions by changing the applied potential discontinuously.
III. Experimental Results
DC Circuits
1.
Verification of Ohm’s Law
In this section, I connected the function generator to the given circuit board to
create a circuit with a known resistor
r
and an unknown resistor
R
connected in series.
Using Labview, I measured the voltage drop across
r
and gained data points to come
up with an experimental value for
R
.
Current vs. Voltage
y = 0.0022x  1E06
2.00E02
1.50E02
1.00E02
5.00E03
0.00E+00
5.00E03
1.00E02
1.50E02
2.00E02
8.00E+0
0
6.00E+0
0
4.00E+0
0
2.00E+0
0
0.00E+00 2.00E+00 4.00E+00 6.00E+00 8.00E+00
Voltage (V)
Current (A)
Since current is constant through resistors in series, I know that calculating the
current through the known resistor will give me the current through the unknown resistor.
Thus when I graph the current through
r
versus the voltage across
R
, I expect a linear plot
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Current vs. Voltage
0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
12
10
8
6
4
2
0
2
Voltage (V)
Current (A)
After Liquid N
At Room Temp
due to the relationship V = IR, where voltage is directly proportional to current. By
obtaining the expected linear plot, I confirmed Ohm’s Law as well as obtained a value for
the slope, or conductance (1/R), which is 0.0022 ohms
1
. Taking the inverse of this value
will give me the experimental value for the unknown resistor.
2.
Resistors in Series and Parallel
For this section, I used a digital multimeter to measure the resistance across each
of three different resistors, two of which were in series and two of which were in
parallel. I then measured the resistance across the resistors in series and then across
the resistors in parallel. By doing this I can compare my calculated values for the total
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 Spring '10
 CARTER
 Resistor, Electrical resistance, Series and parallel circuits

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