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Name: 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 Kr 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)