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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) Show calculation with units: Current necessary for full scale deflection of galvanometer, Ig V Ig = = K+r € Part B: Voltmeter Show calculation with units: Multiplier resistance, M (for a voltmeter with a full scale deflection for 3.0 volts) Eqn 1. M = Vmax −r = Ig WARNING: Set the multiplier resistance to your calculated value BEFORE connecting the power supply as shown in Figure 5-6 in the 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)*** Part C: Ammeter Show calculation with units: Shunt resistance, s (for an ammeter with a full scale deflection for 3.0 A) rI g Eqn 2. s = = I max − I g Lab: Analog Galvanometers Updated 02/06/2017 Data & Reporting score: Show calculation with units: 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) = Have instructor sign off on your wire length BEFORE you make your shunt resistor with the copper wire. __________ Instructor initials. NOTE: 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. SEE THE INSTRUCTOR IF YOU CANNOT FIND THE LENGTH YOU NEED IN THE PILE OF PRECUT WIRE SEGMENTS. Connect your wire shunt resistor to the galvanometer following the lab manual directions (pages 5-5 to 5-6) and Figure 5-7 BEFORE connecting the power supply. Table 3: 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)*** Analysis: 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 such as LINEFIT to plot the following graphs. NO HAND-DRAWN GRAPHS FOR THIS LAB REPORT. Use a computer program to calculate a best-fit line (least squares type fit). Record the resulting slope and y-intercept in Table 4 – round to the thousandths place (e.g., 1.013). Use the same scale (and units) for both yand x-axes. • • Graph 1: Power supply voltage versus galvanometer voltage, V vs. Vgal Graph 2: Power supply current versus galvanometer current, I vs. Igal Lab: Analog Galvanometers Updated 2/06/2017 (“y” vs. “x”) (“y” vs. “x”) (Phy 133L) If you complete both graphs during class period, show the instructor your results on screen and have the instructor initial here. You do not have to print out the graphs for your report with the instructor’s initial below. Instructor’s initial for graphing/least-squares fit during class:__________________ If you do not finish the graphs during class (and have the instructor’s initial), then you must print out both of your graphs and include them with your lab report. Label and title your graphs appropriately either with the computer or by hand after you have printed them out. Include your computer-calculated best-fit line on your graph. [Screen print for LINEFIT is ok – write axis labels, and title by hand.] 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 4: 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 2/06/2017 (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 (b) Are your voltages reading less than or be? (Circle one of the underlined choices.) more than or or No? (Circle one) exactly what they should (c) The observed voltage read on the galvanometer (Vgal) is _________________ proportional to Ig, the galvanometer current for a full-scale deflection. Choose “directly” or “inversely” to fill in the blank in the above sentence. (d) By what percent did you misread Ig in your experiment? (Use the results of your voltage graph to calculate the misread in Ig following the reasoning in the Analysis and Systematic Errors section of the Analog Galvanometer lab in your Lab Manual.) Show your calculation(s) below or state your reasoning. Ig is ____________% too large/too small [Fill in the numerical value and circle whether it is “too large” or “too small] 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 (b) Are your measured current values (Igal) too large or they should be? (Circle one of the underlined choices.) too small (c) Does this mean that your s, the shunt resistant you used, is exactly right ? (Circle one of the underlined choices.) (d) By what percent was your shunt resistance, s, off? Show work below or state your reasoning. or No? (Circle one) or too large or exactly what too small or _________ % (e) Equation 2 tells us that s is _______________ proportional to Igr. Choose “directly” or “inversely” to fill in the blank in the above sentence. (f) 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 following the reasoning in the Analysis and Systematic Errors section of the Analog Galvanometer lab. [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.] - continued on next page - Lab: Analog Galvanometers Updated 2/06/2017 (Phy 133L) Question 3f – continued – By what percent did you misread r in your experiment? Show your calculation(s) below or state your reasoning. r is ____________% too large/too small [Fill in the numerical value and circle whether it is “too large” or “too small] 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. voltage of the thing you are measuring multiplier resistance (M) shunt resistance (s) (b) Use algebra (not your data) and the maximum voltages of the ranges listed in part (a) to calculate by what factor it changes. [Show your work or state your reasoning. You may assume that r << M to cancel a term.] (c) Does it increase or decrease ? (Circle one) 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. current of the thing you are measuring multiplier resistance (M) shunt resistance (s) (b) Use algebra (not your data) and the maximum currents of the ranges listed in part (a) to calculate by what factor it changes. [Show your work or state your reasoning. You may assume that Ig << Im to cancel a term.] (c) Does it increase or decrease ? (Circle one) 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? Consider uncertainty. 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 2/06/2017 (Phy 133L)