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Lab: Series Circuit
Theory:
In 1827, Georg Simon Ohm (1787-1854), a German physicist,
demonstrated a relationship between the current and the potential difference across a
number of different materials. This relationship that he was the first to demonstrate was a
linear relationship, or more specifically, a direct proportion. In honor of Georg Simon
Ohm, this relationship has been named Ohm’s Law.
You will remember that a linear function, when graphed, appears as a straight line. Its
equation can be written in the form y=mx+b. Where y and x are the variables, m is the
slope of the graph line, and b is the vertical axis intercept. When b=0, we refer to the
relationship between the variables y and x as a direct proportion, and the graph of y vs. x
goes through the origin (0,0).
Now, a variable can be any measured quantity that changes. In a simple circuit with a
given load, we may choose to vary the supply voltage so that the voltage (V) becomes a
variable. If we choose to measure the current (I) then it also becomes a variable. In order
to state the relationship between V and I we could write an equation, or write a verbal
description. We might show this relationship visually by graphing V vs. I. Each of these
different types of descriptions of the circuit are known as representations.
We will be using resistors in this lab. Resistors are made to have a particular resistance.
The marking for this rating are in colored bands on the resistor. You will need to learn to
read this color-code to find the “theoretical” or rated value for each resistor.
Reading a resistor color code.
Write the values for R1 here:
1st color
2nd color:
3rd color:
4th color
_________
_________
___________
(gold 5% or
silver 10%)
Numerical
value of
this color
Numerical
value of
this color
Take the numerical
value of the color
and write that
number of zeros.
Resistor value:
Write the resistance
as indicated by the
color bands.
Find the
tolerance for
your resistance
value
Write the values for R2 here:
1st color
2nd color:
3rd color:
4th color
_________
_________
___________
(gold 5% or
silver 10%)
Numerical
value of
this color
Numerical
value of
this color
Take the numerical
value of the color
and write that
number of zeros.
Phy 115: Series Circuit
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Resistor value:
Write the resistance
as indicated by the
color bands.
Find the
tolerance for
your resistance
value
rev. 11/13
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You will need to select two different resistors to use in this lab. Choose two that are
between 1000 and 9000 ohms. Measure the resistance and write the values your meter
indicates.
Procedure:
You will need a simple circuit with a stable supply voltage that can be changed, and two
resistors in series. Select a power supply and 2 resistors, then physically wire the circuit
so that your two resistors are in series. Do NOT turn on your power supply
until the instructor has checked it.
Draw a picture of your circuit. This is not a schematic but an actual sketch of what it
looks like, much like you would see if you took a picture with a camera.
Draw a circuit schematic of this situation.
Calculate the maximum current you expect. Use the rated values for your resistors. Use
this value to make sure that the multimeter that will measure current is correctly
configured.
Add the 2 multimeters (one to measure current and one to measure V) to the picture and
to the schematic you drew. Make sure that your drawing is clear as to how the meter is
hooked into the circuit to make the measurements you want. The symbols are a V or an A
with circles around the letter.
Take several sets of V and I measurements for R1 and for R2 and for the series
equivalent of R1 and R2. Record them in a table that you create. Be sure to:
 Label each measurement with its variable and unit. You should know how to get
information about units from your multimeter.
Phy 115: Series Circuit
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
Include the uncertainty with each type of measurement. Remember that you have
digital meters. You either have a single digital reading where you have the meter
rounding or you have a meter reading that is slightly changing.
Analysis:
Analyze your data so that you will be able to give an answer to the question posed in your
purpose. In the analysis section, be sure to include all of your reasoning. You should have
more than just tables and graphs. If possible, make one graph for all of the results from
your series circuit. This graph should have 3 lines on it. Include words that describe the
relationship that you see. Remember that you have given a prediction in the theory section
of your report. You should compare your results to that prediction and support your
conclusion with reasoning.
Include an uncertainty section. You should be able to use what you learned about derived
uncertainty in this lab to talk about uncertainty of your analysis.
Conclusion:
Conclude by summarizing an answer to the question posed in your purpose. Make your
summary as specific as possible and include a comparison to theory.
Phy 115: Series Circuit
Eyres
rev. 11/13