Name: Dr. Julie J. Nazareth Lab Partner(s): Physics 123L Date lab performed: 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)
Show calculation with units: Current necessary for full scale deflection of galvanometer, Ig V I = = g K + r
Part 2: Voltmeter Show calculation with units: Multiplier resistance, M (for a voltmeter with a full scale deflection € for 3.0 volts)
V Eqn 1. M = max − r = I g
WARNING: Set the multiplier resistance to your calculated value BEFORE connecting the power supply as shown in Figure 2 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)***
Show calculation: For the power supply voltage of 2.0 volts, translate your corresponding galvanometer reading in divisions into voltage in volts. Include uncertainty. Don’t forget units and to round properly.
Lab: Analog Galvanometers Updated 06/01/2017 (Phy 123L) Now measure the voltage on a battery using your galvanometer voltmeter. Disconnect the leads from the power supply and touch to either side of used battery provided by instructor.
Table 3: Measuring the Voltage of a Battery Using a Galvanometer Voltmeter Battery Letter Multimeter voltage reading from instructor (volts) Galvanometer Reading (divisions) Calculated galvanometer battery voltage (volts) Percent difference (%)
Show calculation: Calculate the percent difference between the voltage you calculated from your galvanometer reading and the multimeter voltage reading.
Part 3: Ammeter Show calculation with units: Shunt resistance, s (for ammeter with full scale deflection for 3.0 A) rI s = g = I max − I g
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, 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 (pg. 6-4) and the figure at the top of page 6-5 BEFORE connecting the power supply.
Table 4: Using the Galvanometer as an Ammeter Power Supply Current, I (A) Galvanometer Reading (divisions) Galvanometer 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 6/01/2017 (Phy 123L) Show calculation: For the power supply current of 1.5 A, translate your corresponding galvanometer reading in divisions into current in A. Include uncertainty. Don’t forget units and to round properly.
Questions: 1. Consider a digital multimeter like the desk version you used in the Oscilloscope lab. (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 and the maximum voltages of the ranges listed in part (a) to calculate by what factor “it” changes. To find the factor, take the first case of “it” divided by second case of “it”. You will NOT get any credit for simply dividing the two voltage values. [Show your work. You may assume that r << M to cancel a term.]
Factor = (c) Does “it” increase or decrease ? (Circle one)
2. Consider a digital multimeter like the desk version you used in the Oscilloscope lab. (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 and the maximum currents of the ranges listed in part (a) to calculate by what factor “it” changes. To find the factor, take the first case of “it” divided by the second case of “it”. You will NOT get any credit for simply dividing the two current values. [Show your work. You may assume that Ig << Im to cancel a term in the denominator.]
Factor = (c) Does “it” increase or decrease ? (Circle one)
Don’t forget to write your conclusion paragraph! (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 from the power supply? Consider uncertainty. Are all of your voltage and/or current readings consistently high or consistently low or inconsistent? If the values are consistently high or low, what is the probable source of error (power supply voltage, power supply current, galvanometer, etc.)? Be specific. You might have a different answer for the voltage than the current. Also, how close did your galvanometer voltmeter come to the multimeter voltage reading for the voltage of a battery? Consider percent difference.)
Lab: Analog Galvanometers Updated 6/01/2017 (Phy 123L)