Name:
Lab Partner(s):
Date lab performed:
Dr. Julie J. Nazareth
Physics 123L/133L
Section:
Response of Circuit Elements
Table 1: Resistance and Current Measurements for a Carbon Resistor
Color Code Colors (left to right):
Color Code Numerical Resistance, RCC (Ohms)
Color Code tolerance (%):
Ohmmeter Model
Ohmmeter Resistance, Rm ( Ohms):
Voltage, V (volts)
Current, I ( A)
Voltage, V (volts)
Current, I ( A)
5.0
-0.5
4.0
-1.0
3.0
-2.0
2.0
-3.0
1.0
-4.0
0.5
-5.0
Table 2: Resistance and Current Measurements for a Light Bulb
Ohmmeter Resistance, RM (Ohms):
Voltage, V (volts)
Current, I ( A)
Voltage, V (volts)
Current, I (
5.0
0.8
4.0
0.7
3.0
0.6
2.0
0.5
1.5
0.4
1.3
0.3
1.1
0.2
1.0
0.1
0.9
0.05
A)
Table 3: Voltage and Current Measurements for a given Power Supply Voltage for a Diode
Ohmmeter resistance, RM ( Ohms): Forward =
Reverse =
Forward Bias
Reverse Bias (reverse leads not the diode)
Power Supply
Power Supply
Voltage,
Voltage,
Current,
Voltage,
Voltage,
Current,
VS (volts)
V (volts)
I ( A)
VS (volts)
V (volts)
I ( A)
40
-40
30
-30
20
-20
10
-10
5
-5
3
-3
2
-2
1
-1
Lab: Circuit Elements
Updated 01/15/2015
Graphs: Plot the following graphs on three separate sheets of graph paper.
• Use most of the sheet of paper to draw your graph (spread your data out!)
• Title and label your graph properly.
• When calculating the local slope, draw your line tangent to the curve at the point instructed.
• Put the calculation of the local slope on your graph, in an unused section of the paper.
• The only calculations on the graph should be the slope calculation(s).
• Draw a small box or circle around the points (not data points!) you used to calculate the
slope. Look for where the best fit line goes exactly through a corner of the gridlines. Try to
find two of these points widely-spaced on your line. If not, it is more important to have two
points where the line goes through a corner of the gridlines, than have widely-spaced points.
• If graphs are completed (and required slopes calculated) before leaving class, each
group only needs to complete one set (the instructor must sign off). All lab partners in
the group will receive the same score for the graph and slope calculation potion of the
grade, if sharing graphs. If the graphs are not completed (and required slopes
calculated) before leaving class, then each lab partner must complete their own graphs
to turn in with their lab report.
Graph 1: Plot the voltage versus current (V vs. I) for a Carbon Resistor. Draw a best fit line
to your data points and calculate the slope of the line (dynamic resistance).
Graph 2: Plot the voltage versus current (V vs. I) for a Light Bulb. Sketch a best fit curve to
your data. Choose a “cold” point (near 0.2-0.5 volts) and a “hot” point (near 4-5 volts) on
the curve, mark the points with an “X”, and label them. Draw tangent lines for the “cold”
and “hot” dynamic resistances. For both tangent lines, use two easy and accurate to read
points on the tangent line to calculate the local slope of the particular tangent line.
Table 4: Location of “Cold” and “Hot” points chosen for Graph 2 (light bulb)
“Cold” point location
“Hot” point location
Voltage, VC (V)
Current, IC (A)
Voltage, VH (V)
Current, IH (A)
Graph 3: Plot the measured voltage versus current (V vs. I) for a Diode. (Do not use the
power supply voltage in your graph.) Sketch a best-fit curve to your data. You might get a
plot something like the curve shown below. Determine the dynamic resistance near +1 mA
in the forward bias direction and near -2 volts in the reverse bias direction. Also, label the
areas #1, #2, and #3 on your graph 3 as either “High R” (high resistance) or “Low R” (low
resistance). See the sketch below to see which areas on your graph 3 are #1, #2, and #3.
Area #1: High resistance or low resistance? (Mark on your
graph)
V
#1
#2
I
Area #2: High resistance or low resistance? (Mark on your
graph)
Area #3: High resistance or low resistance? (Mark on your
graph)
#3
Lab: Response of Circuit Elements
Updated 01/15/2015
Calculations: Show the following calculations in the space provided (or on the graph if directed
to do so). This means show what numbers you put into the formula, as well as the decimal
answer with units. Don’t forget to round your final answer properly for calculations of, or with,
uncertainty. For calculations without uncertainty, don’t worry about the significant digits of the
final answer - just be reasonable. Always keep two extra non-significant digits in the middle of
calculations to prevent rounding error. Remember, the only calculations on the graphs (front or
back side) should be slope calculations.
For Part 1, Carbon Resistor
• Determine the color code tolerance in Ohms (decimal form) instead of a percent. Give your
final answer as the color code resistance with uncertainty, properly rounded and with units.
RCC =
•
±
Determine the meter uncertainty in the ohmmeter measurement of the resistance. Give your
final answer as the ohmmeter resistance with uncertainty, properly rounded and with units.
RM =
•
Calculate the static resistance at 3.0 volts, RS = V/I
•
Using graph 1, determine the dynamic resistance, RD = slope of best fit line
(put this calculation on the graph in an unused section of the paper)
±
For Part 2, Light Bulb
• Calculate the “cold” static resistance at your “cold” point listed in Table 4. RCS = VC/IC
•
Calculate the “hot” static resistance at your “hot” point listed in Table 4. RHS = VH/IH
•
Using graph 2, determine the “cold” dynamic resistance, RCD = slope of “cold” tangent line
(put this calculation on the graph in an unused section of the paper)
•
Using graph 2, determine the “hot” dynamic resistance, RHD = slope of the “hot” tangent line
(put this calculation on the graph in an unused section of the paper)
Lab: Response of Circuit Elements
Updated 01/15/2015
For Part 3, Diode
• Using graph 3, determine the dynamic resistance near +1 mA, RFB = slope of tangent line
(put this calculation on the graph in an unused section of the paper)
•
Using graph 3, determine the dynamic resistance near -2 volts, RRB = slope of tangent line
(put this calculation on the graph in an unused section of the paper)
Table 5: Carbon Resistor Resistance Results: Comparing Measurements
Code Resistance,
Ohmmeter Resistance, Static Resistance Dynamic Resistance
RC ( Ohms)
RM ( Ohms)
RS ( Ohms)
RD ( Ohms)
±
±
Table 6: Light Bulb Resistance Results: Comparing Measurements
“Cold” Point
“Hot” Point
Ohmmeter,
Static
Dynamic
Static
Dynamic
RM ( Ohms)
( Ohms)
( Ohms)
( Ohms)
( Ohms)
Table 7: Diode Resistance Results: Comparing Measurements
Dynamic Resistance
Forward Bias
Dynamic Resistance
Reverse Bias
near +1mA, RD1mA
Ohmmeter Resistance,
near -2 V, RD-2V
Ohmmeter Resistance,
( Ohms)
RFB ( Ohms)
( Ohms)
RRB ( Ohms)
Don’t forget to write your conclusion paragraph on an attached sheet of paper!
As always, start with an introductory sentence that tells the reader the purpose/objective of this
particular lab. Some things to consider before writing your conclusion paragraph:
• Does the carbon resistor follow Ohms “Law”? What about your data/results tells you this?
• How do the static and dynamic resistance of the carbon resistor compare with each other?
• How do those values compare with the ohmmeter reading … and the color code?
• Do all of the [carbon resistor] resistances, or only some of them agree within uncertainty?
Be specific and if there are differences between the values, discuss why that might be so.
• Does the light bulb follow Ohms “Law”? What about your data/results tells you this?
• How do the various resistance measurements for the light bulb compare?
• With which resistance measurement from graph 2 (static or dynamic) does the ohmmeter
measurement, RM, most nearly agree? Why do you think that is?
• Does the diode follow Ohms “Law”? What about your data/results tells you this?
• What does the shape of the diode curve (graph 3) tell you about the resistance of and flow of
current through a diode? What was happening to the current flow at #2 on your graph 3?)
(When does current flow and when does it not really?)
Remember, you are NOT answering the above questions individually, and writing them in the
shape of a paragraph. You are writing a continuous, connected, coherent paragraph (or
Lab: Response of Circuit Elements
Updated 01/15/2015
paragraphs) where ideas/sentences are connected and you smoothly flow from one sentence to
the next. If you were to write something like “… Yes, the carbon resistor follows Ohms law.
The static and dynamic resistances are very similar. The ohmmeter and the color code are about
50 Ω apart …”, then you would be turning in a poorly written paragraph. The example given in
the previous sentence is a collection of sentences, only partially answering individual “hint”
questions, without any apparent connection between the ideas. If you didn’t know the lab
experiment, you might not have any idea that the individual sentences had anything to do with
each other. On the other hand, something like the following would be considered the start of a
good conclusion paragraph: “In the Response of Circuit Elements lab, we determined the
resistance of a carbon resistor, a light bulb, and a diode by applying various voltages and
measuring the current flow that resulted. The carbon resistor followed Ohm’s law as shown by
the straight line fit of the graph of voltage versus current. In addition, the static resistance, the
dynamic resistance, the color code resistance, and the ohmmeter resistance all agreed within
uncertainty. In contrast, the graph of voltage versus current for the light bulb showed a curve,
suggesting that the light bulb does not follow Ohm’s law …”
Do
NOT
Write
Your
Conclusion
paragraph(s)
in
this
space !!!!!
Use an attached sheet of paper.
Lab: Response of Circuit Elements
Updated 01/15/2015