19 Sep You are going to investigate the characteristics of circuits with resistors in series and circuits with resistors in parallel. To investigate the characteristics, you are going to appl

Name: __________________________________ Date: ____________________

SERIES AND PARALLEL CIRCUITS

Introduction

In today’s lab, you are going to investigate the characteristics of circuits with resistors in series and circuits with resistors in parallel. To investigate the characteristics, you are going to apply Ohm’s Law.

Voltage (V) = Current (I) x Resistance (R)

Purposes

1. To determine the equivalent resistance of resistors in series.

2. To determine the equivalent resistance of resistors in parallel.

3. To apply Ohm’s Law to simple circuits.

Materials

This lab requires you to create simulated circuits using the PhET Circuit Construction Kit Virtual Lab ( be sure you use the HTML5 version, not the Java version).

Part 1: Applying Ohm’s Law to a Simple Circuit

Create the following simple circuit using the simulation.

The simulation shows electrons flowing from the negative terminal of the battery (black end), through the resistor (light bulb) and the positive terminal (copper colored end).

Change the current direction by selecting Conventional Current (in top right box). This shows the direction physicists thought current was flowing before the existence of the electron was discovered.

Set the voltage and resistance in your circuit using the values in the table below that correspond to the first letter of your last name:

First letter of Last Name	Voltage	Resistance
G-I	7 V	7 Ω

Change the setting on the battery and light bulb by clicking on the component and using the arrows and/or slider at the bottom of the simulation screen. Enter the values you are using in the table below:

Voltage	Resistance	Current
	V		Ω		A

Using your assigned values of voltage (V) and resistance (R), use Ohm’s Law to calculate the current to demonstrate that the ammeter reading is correct.

Result of this calculation =		A

Now double the voltage. Indicate the new values in the circuit in the following table:

Voltage	Resistance	Current
	V		Ω		A

So when the voltage is doubled, the current is (put an X next to your choice)
	a	½ of what it was.
	b	¼ of what it was.
	c	4 times what it was.
	d	2 times what it was.

Do not change the voltage of the battery from new value (listed above). Double the resistance. Indicate in the following table the values of the circuit after making the change.

Voltage	Resistance	Current
	V		Ω		A

So when the resistance is doubled, the current is (put an X next to your choice)
	a	½ of what it was.
	b	¼ of what it was.
	c	4 times what it was.
	d	2 times what it was.

For part 2 and 3, keep the voltage the same as the value you were assigned in part 1. Use the following values of resistances in your circuit using the values in the table below that correspond to the first letter of your last name

First letter of Last Name	Voltage	Resistance 1	Resistance 2
G-I	7 V	7 Ω	10Ω

Part 2: Resistors in Series

In this part of the lab, you are going to create the following circuit with two resistors in series. Set the battery voltage and the value of each resistor to the value you were assigned in part 1.

The equivalent resistance of resistors in series is determined by adding all the resistor values. This is true because the current is the same flowing through each resistor.

Req = R1 + R2

Using the relationship for resistors in series, find the equivalent resistance in the circuit you’ve assembled and record in the table below:

Resistor 1	Resistor 2	Equivalent Resistance
	Ω		Ω		Ω

Record the voltage and current of your circuit.

Voltage	Current
	V		A

Apply Ohm’s Law to your circuit to calculate the current to demonstrate that the ammeter reading is correct ( recall that now R is the equivalent resistance in the circuit).

Result of this calculation =		A

In a series circuit, the sum of the voltage drops across each resistor should equal the voltage of the battery. Using the voltmeter you will demonstrate that this is true for the circuit you’ve created. Record your results in the table below:

R1 Voltage	R2 Voltage	Sum of R1 + R2

Questions

If you were to have three resistors in series, how would you determine the equivalent resistance of the circuit.

Make a statement regarding the voltage drop across each of the three resistors in your new circuit and how it would relate to the voltage of the battery.

Part 3: Resistors in Parallel

In this part of the lab, you are going to explore the characteristics of a circuit with resistors in parallel. Use your assigned values for battery voltage and resistance to assemble the circuit shown below ( notice the use of additional ammeters):

In a parallel circuit, the voltage drops across each resistor should equal the voltage of the battery. Using the voltmeter you will demonstrate that this is true for the circuit you’ve created. Record your results in the table below:

R1 Voltage	R2 Voltage	Battery Voltage

The current through each resistor is affected by the branching in the parallel circuit. In the table below, record the current coming out of the battery, the current going into each resistor and the current flowing back to the battery.

Current Out of Battery	Current to R1	Current to R2	Current Into Battery

Since the voltage across each resistor in a parallel circuit is the same, we approach finding the equivalent resistance from the sum of the currents. This gives the following relationship for calculating the equivalent resistance in a parallel circuit.

Using the relationship for resistors in parallel, find the equivalent resistance in the circuit you’ve assembled and record in the table below:

Resistor 1	Resistor 2	Equivalent Resistance
	Ω		Ω		Ω

Apply Ohm’s Law to your circuit to calculate the current to demonstrate that the ammeter reading is correct ( recall that now R is the equivalent resistance in the circuit).

Result of this calculation =		A

Questions

If you were to have three resistors in parallel, how would you determine the equivalent resistance of the circuit.

Make a statement regarding the voltage drop across each of the three resistors in your new circuit and how it would relate to the voltage of the battery.

Make a statement regarding the current through each of the three resistors in your new circuit and how it would relate to the overall current.

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