Name:

Date: Period:

Background:A series circuit consists of resistors connected with the voltage source in such a way that the total current must flow through each resistor in turn. The effective resistance of a series circuit is the sum of the resistances of the individual resistors in the circuit.

Throughout this lab, you will apply Ohm’s Law:
Objective: During this investigation you will use Ohm’s Law to determine the effective resistance in series circuits. /

Above, The circuit diagram for measuring the current and voltage across (a) one resistor, (b) two resistors, (c) three resistors in series.
Right, The apparatus is connected
for three resistors in series
Materials:
Power supply
6 “banana” leads
4 Alligator clips
3 resistors
1 Ammeter
1 Voltmeter
Switch /
.

Procedure:

A. One Resistor

  1. Arrange the single resistor in series with the ammeter, open switch, and voltage source as in Figure (a). Arrange the voltmeter in parallel with the resistor as shown in the figure. 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 in Table 1.

B. Two Resistors

  1. Arrange two resistors in series with each other. Connect the resistors in series with the ammeter, open switch, and voltage source and in parallel with the voltmeter as in Figure (b). Keep the voltage at approximately 6 volts.
  2. Close the switch long enough to read the meters and record your observations in Table 2.

C. Three Resistors

  1. Arrange three resistors in series with each other. Connect the resistors in series with the ammeter, open switch, and voltage source and in parallel with the voltmeter, as in Figure (c). Keep the voltage at approximately 6 volts.
  2. Close the switch long enough to read and record your meter readings in Table 3.
  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 resistor R1, close the switch, and read the meter. Record the reading in Part C of the Data and Calculations.
  4. Repeat Step #3 for R2 and R3.

Data and Calculations:

A. One Resistor

1. Printed value of R1

Table 1:One Resistor

Ammeter Reading (A) / Voltmeter Reading (V)

2. Measured value of

B. Two Resistors

1. Printed value of R1 and R2

2. Calculated equivalent resistance (R1+R2) =

Table 2:Two resistors

Ammeter Reading (A) / Voltmeter Reading (V)

3. Measured value of

C. Three Resistors

1. Printed value of R1 , R2 and R3

2. Calculated equivalent resistance (R1+R2+R3) =

Table 3:Three resistors

Ammeter Reading (A) / Voltmeter Reading (V)

3. Measured value of

4. Total measured voltage drop across the three resistors (V1+V2+V3) =

Conclusion Questions:

  1. When a circuit consists of resistors in series, how is the equivalent resistance determined?
  1. How are the voltage drops across individual resistances related to the total voltage drop in a series circuit?
  1. What determines the total current in a series circuit?
  1. How is Ohm’s Law applied to find the current in a series circuit?
  1. A circuit contains four 15 Ω resistors connected in series. What is the equivalent resistance of the circuit?
  1. The circuit of #5 is placed across a 120 V source.
  2. What current will flow in the circuit?
  1. What will be the voltage drop across each resistor?
  1. A 15 Ω resistor, a 10 Ω resistor and a 5 Ω resistor are connected in series and then placed across a 45 V source.
  2. What is the equivalent resistance of the circuit?
  1. What current flows in the circuit?
  1. What is the voltage drop across each resistor?