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Lab Partner(s):
Date lab performed:
Dr. Julie J. Nazareth
Physics 133L
Section:
Analog Galvanometers
Part 1: Galvanometer Characteristics
Table 1: Galvanometer Characteristics
Resistance of series resistor, K (Ohms)
Voltage at full scale deflection, V (volts)
Resistance at half scale deflection, h (Ohms)
Current necessary for full scale deflection, Ig ( A)
Calculation: Current necessary for full scale deflection of galvanometer, Ig
V
Ig 

Kr

TURN ALL POWER SUPPLY DIALS COUNTERCLOCKWISE (LEFT). TURN THE
POWER OFF AND DISCONNECT ALL LEADS.
Part 2: Voltmeter
Calculation: Multiplier resistance, M (for a voltmeter with a full scale deflection for 3.0 volts)
Eqn 1. M 
Vmax
r 
Ig
SET THE MULTIPLIER RESISTANCE TO YOUR CALCULATED VALUE BEFORE
CONNECTING THE POWER SUPPLY. CONSTRUCT THE VOLTMETER FOLLOWING
FIGURE 6 IN LAB MANUAL.
Table 2: Using the Galvanometer as a Voltmeter
Power Supply Voltage,
Galvanometer
Galvanometer
V (Volts)
Reading (divisions) Voltage, Vgal (Volts)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Lab: Analog Galvanometers
Updated 02/01/2013
Data & Reporting score:
NOW MEASURE THE VOLTAGE ON A BATTERY USING YOUR GALVANOMETER
VOLTMETER. TURN ALL POWER SUPPLY DIALS COUNTERCLOCKWISE (LEFT).
TURN THE POWER OFF AND DISCONNECT LEADS FROM POWER SUPPLY ONLY.
USE LEADS THAT USED TO ATTACH TO POWER SUPPLY TO MEASURE VOLTAGE
ACROSS THE BATTERY. AFTER THE MEASUREMENT, DISCONNECT ALL LEADS.
Table 3: Measuring the Voltage of a Battery Using a Galvanometer Voltmeter
Battery # or letter
Multimeter voltage reading from instructor (volts)
Galvanometer Reading (divisions)
Calculated (galvanometer) battery voltage (volts)
Percent difference (%)
Part 3: Ammeter
Calculation: Shunt resistance, s (for an ammeter with a full scale deflection for 3.0 A)
rI g

Eqn 2. s 
I max  I g
Calculation: Length of piece of #22 copper wire with resistance, s, calculated above. (#22
copper wire resistance = 0.00053 Ω/cm) Show full calculation below, not just answer.
Wire length = resistance / (resistance per length) =
__________ Instructor initials.
THE ABOVE LENGTH IS FOR THE BENT PART OF THE WIRE SHUNT RESISTOR.
YOU NEED 2-3 CM ON EITHER SIDE OF THE BENT PART TO ATTACH THE
ALLIGATOR CLIPS FROM THE LEADS. LOOK TO SEE IF THERE IS ANY PRECUT
COPPER WIRE 4-6 CM LONGER THAN YOUR CALCULATED LENGTH BEFORE
CUTTING NEW WIRE. IF YOU HAVE TO CUT NEW WIRE, HAVE THE INSTRUCTOR
APPROVE YOUR CALCULATED LENGTH BEFORE CUTTING ANY COPPER WIRE.
CONNECT YOUR WIRE SHUNT RESISTOR TO THE GALVANOMETER FOLLOWING
LAB MANUAL DIRECTIONS (PG. 5-5 to 5-6) BEFORE CONNECTING THE POWER
SUPPLY. CONSTRUCT THE AMMETER FOLLOWING FIGURE 8 IN LAB MANUAL.
Table 4: Using the Galvanometer as an Ammeter
Power Supply Current,
Galvanometer
Galvanometer
I (A)
Reading (divisions)
Current, Igal (A)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Lab: Analog Galvanometers
Updated 02/01/2013
(Phy 133L)
Part 4: Identifying any systematic errors
BE SURE TO READ/FOLLOW THE ANAYLSIS DESCRIBED IN THE LAB MANUAL
UNDER THE SECTION TITLED: Analysis and systematic errors. (Make sure you turn the
page to read the last paragraph on page 5-8!)
Graphs: Use a computer program or hand-draw the following graphs. Use a computer (or
calculator) program to calculate a best-fit line (least squares type fit). Record the resulting
slope and y-intercept in Table 5. Use the same scale (and units) for both y- and x-axes. If using
a computer program to draw the graph, make sure it prints out with the same scaling for x- and yaxes (1:1). Label and title your graphs appropriately. Include your computer-calculated best-fit
line on your graph. [Screen print for LINEFIT is ok – write labels, title by hand.]
 Graph 1: Power supply voltage versus galvanometer voltage, V vs. Vgal
 Graph 2: Power supply current versus galvanometer current, I vs. Igal
NOTE: If you choose to ignore any data points for cause (outliers) when the computer (or
calculator) calculates the slope and y-intercept, be sure to record this on your data sheet and
circle the ignored data points on your graph. (Yes, graph all data and only circle the points on
the graph if you have treated them as outliers to be ignored in your calculation of the best-fit
line).
Table 5: Graphing Results
Slope
Y-intercept values
Y-intercept units
Graph 1
(Voltage)
Graph 2
(Current)
Questions: Answer the following questions in the space provided.
[Questions below directly copied or modified from the Physics 133L Laboratory Manual
(revision 5/09) Analog Galvanometer Experiment]
1. Do either or both graphs have a non-zero intercept? If yes, which meter (galvanometer,
power supply voltmeter, power supply ammeter) is most likely to have caused your observed
non-zero intercept values? Why do you think that? How much is this meter misadjusted?
Be specific.
Lab: Analog Galvanometers
Updated 02/01/2013
(Phy 133L)
2. Consider your voltmeter graph.
(a) Does the slope of the voltmeter best-fit line differ from one? _____________________
If the answer should be “yes” in (a), please do the following analysis/answer the following
questions.
(b) Are your voltages reading less than or more than they should be? ____________________
(c) The voltage read (Vgal) is _________________ proportional to Ig, the galvanometer current
for a full-scale deflection. [Choose “directly” or “inversely” to fill in the blank.]
(d) By what percent did you misread Ig in your experiment? _____________ too large/too small
[Fill in the numerical value and circle whether it is “too large” or “too small”. State your
reasoning or show work to support your answer.]
3. Consider your ammeter graph.
(a) Does the slope of the ammeter best-fit line differ from one? ______________________
If the answer should be “yes” in (a), please do the following analysis/answer the following
questions.
(b) Is your measured current (Igal) too large or too small? ____________________________
(c) Does this mean that your s, the shunt resistant you used, is too large or too small?
_______________________
(d) Equation 2 tells us that s is _______________________ proportional to Igr. [Choose
“directly” or “inversely” to fill in the blank.]
(e) We can rewrite this to say that r is proportional to s/Ig. Use the percent misreads in s and Ig
to estimate the misread in r. [Remember, if something is say 2% too small, we write that as
98% of what it should be, or .98 in decimal form, while something that is 2% too large is
102% of what it should be, or 1.02 in decimal form.] Show your work here (or state your
reasoning).
By what percent did you misread r in your experiment? _____________ too large/too small
[Fill in the numerical value and circle whether it is “too large” or “too small”.]
Lab: Analog Galvanometers
Updated 02/01/2013
(Phy 133L)
4. Consider a digital multimeter like the desk version shown in figure 9 on page 5-8.
(a) What changes inside when you push the button to change from the 200V range to the 20V
range? Be specific in the name of this something. [Hint: Consider what we were combining
with the analog galvanometer to measure voltage.]
(b) By what factor does it change and does it increase or decrease? [Show your work or state
your reasoning.]
5. Consider a digital multimeter like the desk version shown in figure 9 on page 5-8.
(a) What changes inside when you push the button to change from the 20 mA range to the 200
mA range? Be specific in the name of this something. [Hint: Consider what we were
combining with the analog galvanometer to measure current.]
(b) By what factor does is it change and does it increase or decrease? [Show your work or state
your reasoning.]
Extra Credit question: Answer Question 4 from the lab manual on a separate sheet of paper and
label it “Extra Credit Question”
Don’t forget to write your summary! (Start with an introductory sentence stating the
purpose/goal(s) of the lab. Did your readings of voltage and current from your galvanometer
come close to the standard readings (consider percent difference of battery voltage)? If you had
any systematic errors, discuss the probable source(s) of these errors. Consider your answers to
questions 1-3, and any misreads you had in Ig and/or r. Be specific and concise.)
Lab: Analog Galvanometers
Updated 02/01/2013
(Phy 133L)