Name: Dr. Julie J. Nazareth
Assignment Partner(s) (if any): Physics 123L/133L
Date assignment performed: Section:
Furlough Day Alternative Assignment - Analog Galvanometers
Be sure to read the entire Analog Galvanometer lab in the lab manual including procedure and analysis – all of the material is fair game for the final exam. I also recommend that you read the part of your lecture textbook that discusses analog galvanometers. Students are encouraged to work together, but each student must turn in their own assignment written in their own words (make sure answers do not sound like your partner’s, or neither will receive credit). This assignment will have equivalent points value of a regular lab report.
Answer the following questions on an attached sheet of paper. For schematic diagrams, be sure to label your diagram appropriately, including word title and direction of current flow. Draw your galvanometer symbol as shown in the lab manual (a zigzag line directly connected to a G). Show all work for calculations. Be sure to include SI units and round to the appropriate number of significant digits in the very last step of the calculation (but keep 2 extra non-significant digits during intermediate steps of the calculation).
1. What is the purpose of, goal of, or reason for doing the Analog Galvanometer lab? (Write your answer as if it were the introductory sentence of a conclusion/summary paragraph).
2. What is an analog galvanometer? How does it physically work?
3. What does a voltmeter measure? (Don’t say volts! Be specific.)
4. Can a galvanometer measure the voltage without an external resistor? Explain
5. Why would we want to use an external resistor in conjunction with the galvanometer to measure voltage? Be specific.
6. Do we want this external resistor to have large or small resistance (to measure voltage)? How specifically does the ______resistance external resistor help us get the voltage range we want for our voltmeter?
7. How would we hook up the external resistor with the galvanometer (to function as a voltmeter) - in series or in parallel?
8. Draw a schematic diagram of the galvanometer with external resistor, and battery (DC power supply) that you are measuring with your galvanometer voltmeter.
9. What does an ammeter measure? (Don’t say Amps. or Amperes! Be specific.)
10. Can a galvanometer measure the current without an external resistor? Explain.
11. Why would we want to use an external resistor in conjunction with the galvanometer to measure current? Be specific.
12. Do we want this external resistor to have large or small resistance (to measure current)? How specifically does the ______resistance external resistor help us get the range in current we want for our ammeter?
13. How would we hook up the external resistor with the galvanometer (to function as an ammeter) - in series or in parallel?
14. Draw a schematic diagram of the galvanometer with external resistor, and battery (DC power supply) that you are measuring with your galvanometer-ammeter.
15. Calculation: A galvanometer has a full-scale current of 0.100mA and a coil resistance of 50.0 Ω (Ohms). This instrument is used with a shunt resistor to form an ammeter that will register full scale for a current of 60.0 mA. Determine the resistance of the shunt resistor.
16. Calculation: A voltmeter utilizes a galvanometer that has a 180.0-Ω coil resistance and a full-scale current of 8.30 mA. The voltmeter measures voltages up to 30.0 V. Determine the external resistance that is connected to the galvanometer. (Hint: Is the external resistance connected in series or parallel with the galvanometer?).
17. Calculation: The coil of a galvanometer has a resistance of 20.0 Ω, and its meter deflects full scale when a current of 6.20 mA passes through it. To make the galvanometer into an ammeter, a 24.8 mΩ shunt resistor is added to it. What is the maximum current that this ammeter can read?
18. Calculation: The equivalent resistance of a voltmeter is 140,000.0 Ω. The voltmeter uses a galvanometer that has a full-scale current of 180 μA (micro-Amps.). What is the maximum voltage that can be measured by the voltmeter?
19. Calculation: When an external resistance of 1680 is connected to a galvanometer, the galvanometer-voltmeter measures voltages up to 20.0 V. When an external resistance of 2390 is connected instead to the same galvanometer, the voltmeter measures voltages up to 30.0 V. Determine the coil resistance and the full-scale current of the galvanometer used in the voltmeter. (Hint: Do no use the formula for Ig in step 1 in the lab manual because the procedure is slightly different between this question and the lab manual. Use the V = IR relationship, and the idea of equivalent resistance.)
20. In measuring a voltage, a voltmeter must use some current from the circuit. Consequently, the voltage measured is only an approximation to the voltage present when the voltmeter is not connected. Consider a circuit consisting of two 1550 Ω resistors connected in series across a 60.0 V battery. (a) Find the voltage across one of the resistors. (b) A voltmeter has a full-scale voltage of 60.0 V and uses a galvanometer with a full-scale deflection of 5.00 mA. Determine the voltage this voltmeter registers when it is connected across the resistor used in part (a). (Hint: Current flow from battery is different with voltmeter connected.)
Furlough day alternative assignment – Analog Galvanometers 10/21/2009