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FULLERTON HIGH SCHOOL PHYSICS MR. GIANNETTI, ROOM # 21 LAB # 28 – RESISTORS IN SERIES – Chapter #19 (7/08) Objective: Using three different resistors to determine how these resistances combine when they are connected in series. Throughout the investigation you will apply Ohm's law: I = V/R Circuit diagram for measuring the current and voltage through (a) one , (b) two, and (c) three resistors in series. R1 = 30 Ohms R2 = 15 Ohms R3 = 10 Ohms PROCEDURE A. One Resistor 1. Arrange the single resistor in series with the ammeter and voltage source as in Figure (a). Set the voltage source at 6 volts or as close to it as your source allows. 2. After your instructor has checked your circuit, close the switch and read the meters. Open the switch as soon as your readings are complete. Record your observations on the data sheet. B. Two Resistors 1. Arrange two resistors in series with each other. Connect the resistors in series with the ammeter and voltage source as in Figure (b). Keep the voltage at approximately 6 volts. 2. Close the switch long enough to read and record your observations on the data sheet. C. Three Resistors 1. Arrange three resistors in series with each other. Connect the resistors in series with the ammeter and voltage source as in Figure (c). Keep the voltage at approximately 6 volts. 2. Close the switch long enough to read and record your observations on the data sheet. 3. With the three resistors still in series, use the voltmeter to find the voltage drop across each resistor. Touch the lead wires of the voltmeter to each end of a resistor and read the meter. Record the reading in Part C of the data sheet. 4. Move the lead wires to the second resistor and determine the voltage drop. Record your observations in Part C of the data sheet. 5. Move the lead wires to the third resistor and determine the voltage drop. Record your observations in Part C of the data sheet. 6. Place the lead wires across all three resistors. Record your observations on the data sheet. DATA AND OBSERVATIONS Part A 1. The current flowing through the resistor is ____________________amperes. 2. The reading of the voltmeter is ______________volts 3. The resistance of the resistor is __________volts divided by_________amperes or _____________ ohms. 4 The known value of the resistor is _________________ ohms. Part B 1. The voltage across the two resistors is __________________ volts. 2. The current flowing through the two resistors is ____________________ 3 The resistance of the two resistors in series is________volts divided by_________amperes or ______________ohms 4. The sum of the known values of the two resistors is __________ohms. Part C 1. The voltage across the three resistors is ______________________ volts. 2. The current flowing through the three resistors is ____________________ amperes. 3. The resistance of the three resistors in series is ______volts divided by ________ amperes or ______________ohms 4. The sum of tile known values of the three resistors is ___________________ ohms. 5. The voltage across R1 = _____________________ volts. 6. The voltage across R2 = ______________________ volts. 7. The voltage across R3 = ______________________ volts. 8. The total voltage drop across the three resistors = V1 + V2 + V3 = ______________Volts____________________ 9. The voltage as measured directly across the three resistors is _________ Volts Interpretations: 1. When a circuit consists of resistors in series the total resistance of the circuit is equal to _________________ 2. When a circuit consists of resistors in series the sum of the voltage drops across the individual resistors is equal to __________________________ 3. The current flowing in a circuit containing resistors in series is equal to the ____________across the entire circuit divided by the ______________of the entire circuit. 4 The resistance of a circuit containing resistors in series is equal to the ____________ across the entire circuit divided by the ______________flowing in the circuit. 5. A circuit contains four 15-ohm resistors connected in series. What is the total resistance of the circuit? 6.. The Circuit of Question 5 is placed across a 120-volt source. (a) What current will flow in the circuit? (b) What will be the voltage drop across each resistor? 7. A 15 ohm resistor, a 10-ohm resistor, and a 5-ohm resistor are connected in series and then placed across a 45 volt source. (a) What is the total resistance of the circuit? (b) What current flows in the circuit? (c) What is the voltage drop across each resistor? DESCRIPTION POINTS Pre Lab 10 PRE-LAB (To be completed in advance). Title page 2 Lab station number 3 Answer the following questions related to this lab. Partners 2 Objective/purpose 4 (a) For three resistors in series, may you Summary 5 Equipment 5 measure the voltage drop across each Procedure 10 resistor with only one volt-meter? How? List known values of resistors 5 Table of results 13 (b) Approximately how high will the input Questions (7) 28 voltage be? Conclusions 8 Neatness 5 TOTAL 100