# Series & Parallel Resistances - Genecon Version

## Purpose:

• to determine the equivalent resistance of two resistors in series
• to determine the equivalent resistance of two resistors in parallel
• to practice constructing electric circuits
• to practice using an ammeter and a voltmeter

## Discussion:

In this lab, you will construct simple circuits using combinations of known resistances in series and in parallel. Then you will use an ammeter to measure the current, I, through the resistor arrangement and a voltmeter to measure the potential difference, V, across it. With this data, you determine the equivalent resistance of the arrangement using Ohm's Law (V = IR) and compare this to the separate resistor values.

## Genecontm generator 5 connecting wires 2 - 3 , 5 Watt resistors 2 - 5 , 5 Watt resistors 2 10 , 5 Watt resistors 2 - 25 , 5 Watt resistors 0-1 A ammeter 0-3 V voltmeter   Procedure:

### Resistors in Series:

1. Choose 2 resistors R1 and R2, and enter their values in the data table.
2. Predict the equivalent resistance of these two resistors in series, and enter your prediction in the data table.
3. Wire this series resistor combination into the circuit shown below. Here's how:
1. Construct the same circuit (one resistor) that you built for the Ohm's Law experiment.
2. Clip one end of a new wire to one end of your second resistor.
3. Clip the other end of this new wire to one end of the resistor you placed in the circuit.
4. Move any wires that were on the resistor in the circuit to the free end of the second resistor.
5. You should be able to trace a conducting path from one clip of the Genecontm generator, through one resistor then through the other, through the ammeter, and back to the generator.
6. Check to be sure that the voltmeter is attached across both resistors.
4. Record the current through the resistor combination and the voltage across it in the data table.

### Resistors in Parallel:

1. Choose 2 resistors R1 and R2 of equal value, and enter their values in the data table.
2. Predict the equivalent resistance of these two resistors in parallel, and enter your prediction in the data table.
3. Wire this parallel resistor combination into the circuit shown below. Here's how:
1. Remove the second series resistor and restore the circuit to the one you built in the Ohm's Law experiment.
2. Clip a new wire to each end of the second parallel resistor.
3. Clip the other end of each new wire to an end of the original resistor in the circuit.
4. Record the current through the resistor combination and the voltage across it in the data table.

## Results:

1. For each trial, calculate the equivalent resistance of the resistor combination based on the measured current and voltage using Ohm's Law. Record your results in your data table, and be sure to show a sample calculation.

## Conclusions:

1. How do you find the equivalent resistance for two resistors in series?

2. How do you find the equivalent resistance for two resistors in parallel?

last update April 12, 2007 by JL Stanbrough