Name:
Lab Partner(s):
Date lab performed:
Dr. Julie J. Nazareth
Physics 133L
Section:
Analog Galvanometers
Part A: 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 B: Voltmeter
Calculation: Multiplier resistance, M (for a voltmeter with a full scale deflection for 3.0 volts)
Eqn 1.
SET THE MULTIPLIER RESISTANCE TO YOUR CALCULATED VALUE BEFORE
CONNECTING THE POWER SUPPLY. CONSTRUCT THE VOLTMETER FOLLOWING
FIGURE 5-6 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
***Galvanometer voltage, Vgal = (# divisions) (Vmax/500 divisions)***
Lab: Analog Galvanometers
Updated 02/07/2015
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 C: Ammeter
Calculation: Shunt resistance, s (for an ammeter with a full scale deflection for 3.0 A)
Eqn 2.
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 5-8 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
***Galvanometer current, Igal = (# divisions) (Imax/500 divisions)***
Lab: Analog Galvanometers
Updated 2/07/2015
(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. Use the analysis and
examples discussed on those pages to answer questions 1-3 below. The computer graphs
and these questions are worth a significant proportion of the lab grade for this report.
Graphs: You should use a computer program to plot 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. Label
and title your graphs appropriately. Include your computer-calculated best-fit line on your
graph. [Screen print for LINEFIT is ok – write axis labels, and title by hand.]
• Graph 1: Power supply voltage versus galvanometer voltage, V vs. Vgal
(“y” vs. “x”)
• Graph 2: Power supply current versus galvanometer current, I vs. Igal
(“y” vs. “x”)
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).
***Round your slope values to the thousands place (e.g., 1.013)***
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 Fall 2014) Analog Galvanometer Experiment]
1. a. Do either or both graphs have a non-zero intercept? Circle one of the following.
Both graphs
Just the voltage graph
Just the current graph
Neither graph
b. If yes, which meter (galvanometer, power supply voltmeter, power supply ammeter) is most
likely to have caused your observed non-zero intercept values? Circle one of the following.
Galvanometer
power supply voltage reading
power supply current reading
c. How much is this meter misadjusted? Be specific. Give values in divisions, volts and/or
amps as appropriate for your answers in 1a and 1b.
Lab: Analog Galvanometers
Updated 2/07/2015
(Phy 133L)
2. Consider your voltmeter graph. Slope rounded to the thousandths place = ____________
(a) Does the slope of the voltmeter best-fit line differ from 1.000? Yes or No? (Circle 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 below to support your answer.]
3. Consider your ammeter graph. Slope rounded to the thousandths place = ____________
(a) Does the slope of the ammeter best-fit line differ from 1.000? Yes
or
No? (Circle 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 2/07/2015
(Phy 133L)
4. Consider a digital multimeter like the desk version shown in Figure 5-9 on page 5-8.
(a) What changes inside the digital multimeter when you push the button to change from the
200V range to the 20V range? Circle one of the following. (Fill in the blank if appropriate.)
voltage of the thing you are measuring
multiplier resistance
shunt resistance
None of these – the ______________________________________________ changed
(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 5-9 on page 5-8.
(a) What changes inside the digital multimeter when you push the button to change from the 20
mA range to the 200 mA range? Circle one of the following. (Fill in the blank if appropriate.)
current of the thing you are measuring
multiplier resistance
shunt resistance
None of these– the ______________________________________________ changed
(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 power supply readings? How well did you measure the 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 2/07/2015
(Phy 133L)