Materials Included In Kit

Additional Materials Required

Safety Precautions

Do not directly connect the positive and negative battery terminals without a load in between. The battery can discharge quickly and the terminals and alligator clips can become very hot. Please follow all laboratory safety guidelines.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of 3 or for 10 student groups.
• Six connector cords should be enough for Design Challenge 1 and five or six for Design Challenge 2, depending on the solution configuration. If single battery holders are used and cannot be snapped together, then an additional connector cord may be required to create a 3-V power supply.
• The miniature lightbulbs included in the kit are rated for 1.2 V. In Part B, with just one lightbulb and switch in the circuit, only a 1.5-V power source should be used or the light may burn out. In Part C, the added resistance of the SPDT switch and the coupler requires a 3-V power source, or the bulb may be extremely dim.
• Any type of 1.5-V batteries may be used. A convenient double battery holder for size D batteries is available from Flinn Scientific, Catalog No. AP9275.

Teacher Tips

• Use this activity with your electricity unit to introduce STEM education and the difference between scientific inquiry and engineering design.
• If time allows, let students try both challenges for more practice in the engineering design process.

Answers to Prelab Questions

1. Examine the circuit diagram in Figure 4.
   {14072_PreLabAnswers_Figure_4}
   1. List the components that make up the circuit.

      Battery, connecting wires, switch (SPST) and lightbulb.

   2. Which type of circuit is represented in the diagram, open or closed?

      The diagram represents an open circuit.

2. For each statement that follows, indicate whether a series or parallel circuit is described.
   1. The current has only one pathway to flow from a battery, through two bulbs and back to the battery.

      Series circuit

   2. The current has multiple pathways through which it can travel.

      Parallel circuit

   3. Two bulbs of equal resistance are connected in a circuit to a 6-V battery. The voltage drop across each bulb is 6 volts.

      Parallel circuit

   4. Two bulbs of equal resistance are connected in a circuit to a 6-V battery. The voltage drop across each bulb is 3 volts.

      Series circuit

3. Examine the circuit drawings and diagrams in Figures 1 and 2.
   1. How are the drawings and the diagrams alike?

      The same circuit components are represented in each. The components are in the same order in the circuit.

   2. How are they different?

      Symbols are used to represent the circuit components in the diagrams, where the components look more like the actual item in the drawings. The connecting wires in the drawings are curved and in the diagrams they are straight with 90-degree turns.

Sample Data

Part A.

Observations

Part B.

Draw a circuit diagram for the circuit with the battery, bulb and SPST switch. Part C.

Draw a circuit diagram for the circuit with the battery, bulb and SPDT switch.

Answers to Questions

Engineering Design and Procedure

1. Consider the challenge assigned to your group. What is the problem you are designing a solution for?

   Challenge 1: The problem is to design a circuit with one lamp controlled by a switch while a second lamp will remain on at all times, even when the lamp is turned off by the switch.
   
   Challenge 2: The problem is to design a circuit with two switches that control one light. If the light is off, flipping either switch will turn it on. If the light is on, flipping either switch will turn it off.

2. Consider the circuit models built in parts A and B.
   1. What type of circuit will the challenge require?

      Challenge 1 will require a parallel circuit. The lamp controlled by the switch will be in series with the switch, but in parallel with the second lamp.
      
      Challenge 2 will require that the light be in series with the switches. When the circuit is complete, the current only has one pathway. Flipping a switch either opens the circuit or directs the current to a different pathway.

   2. What type of switch(es) will the challenge require?

      Challenge 1 will require an SPST switch.
      Challenge 2 will require two SPDT switches.

   3. Will any couplers be needed?

      Challenge 1 will require a coupler for the parallel circuit.
      Challenge 2 will not require a coupler.

6. Draw the circuit diagram on a clean sheet of paper and attach it to the worksheet.

   Possible solution to Challenge 1:

   {14072_Answers_Figure_1}

   Possible solutions to Challenge 2:

   {14072_Answers_Figure_2and3}

Post-Lab Questions

1. For Part A, explain the difference in brightness between the bulbs in the series circuit and the bulbs in the parallel circuit.

   Since the effective resistance is lower in the parallel circuit, the total current is greater in the parallel circuit than in the series circuit with the same power source and load. A greater current results in greater brightness of the bulbs.

2. List the constraints given for your design challenge.

   No more than 3 V is to be used as the power source. If using 1.5-V batteries, then two batteries combined are considered one power source with one positive and one negative terminal. Only one alligator clip may be attached to the positive terminal and one clip to the negative terminal of the power supply. A maximum of six connector cords may be used.

3. In completing your challenge, explain how you followed the engineering design process as shown in Figure 9.

   The problem was defined and possible solutions were considered. One solution was selected and the circuit was built. The circuit was tested and evaluated to make sure it met the design criteria and constraints.

4. Compare your challenge solutions to other groups with the same challenge. Did any group have a different solution than yours?

   Answers will vary. Alternative solutions to Challenge 2 are provided in the Engineering Design and Procedure answers.

5. For each of the following questions, determine if it is a scientific question or an engineering problem.
   1. Is lightning a form of electricity?

      Scientific question

   2. How are current, voltage and resistance in a circuit related?

      Scientific question

   3. How can a microwave be added to a kitchen without overloading the circuit?

      Engineering problem

   4. How can a string of holiday lights be designed to blink on and off in time with music?

      Engineering problem

Introduction

Wiring electric circuits in a house requires knowledge of science, engineering, math and technology. These four fields together are known by the acronym, STEM. Apply science and engineering concepts by making models of electric circuits that one might find in a typical home.

Concepts

• Engineering design
• Circuits
• Electricity
• Circuit diagrams

Background

Energy is the ability to do work or cause change. When an object does work on another object, some of the energy of the working object is transferred to that object. One type of energy is electric energy (energy of moving electrical charges). Work in an electrical system is done by moving negatively charged particles called electrons. The movement of electrons in an electrical system is called electric current. To generate an electric current, energy must be supplied to the electrons. This supplemental energy can be chemical, such as a battery, or mechanical, such as water, wind or steam turning a generator. The amount of energy supplied to each electron passing through the electrical system is called voltage. In order for electrons to move from an area of high voltage to an area of low voltage, there must be an unbroken pathway. This pathway is known as a circuit. In a simple circuit, the necessary components include a source of voltage, a conductor—a material in which electrons can move easily—and a device or load to use the electrical energy. A closed circuit is one in which no break occurs in the pathway and the current flows. If a break occurs anywhere in the pathway, then no current flows; this is an open circuit. Table 1 shows common symbols used in circuit diagrams to represent components in a circuit.

A circuit powered by a battery uses direct current (DC). In a simple DC circuit, a load, such as a lightbulb, is connected between the terminals of the battery with conductive wires. When the circuit is closed, the electrons travel from the battery through the load, providing energy to the load, and back to the other battery terminal. The amount of work done on each load is determined by the voltage drop across it. The voltage drop is the energy removed from the electrical system per unit of charge passing through the load, and depends upon the resistance of the load. Resistance is a measure of how difficult it is for the electrons (current) to travel through a load. The filament in an incandescent bulb has high resistance; therefore, the energy from the flowing electrons causes the filament to heat up and produce visible light. If more than one load is connected in a circuit, the energy is distributed throughout all the loads, depending upon the number of loads and how they are connected in the circuit. There are two ways to connect loads in simple DC circuits—in series and in parallel.

In a series circuit (see Figure 1), all of the loads are connected together in a line from the negative terminal to the positive terminal of the electric power supply (battery). The current has only one path to travel; therefore, the current is the same through each load. The higher the total resistance in a circuit, the lower the total current will be traveling through the circuit and through each load. The voltage in a series circuit is the same as the sum total of the voltage drops across each load. Loads connected in parallel circuits are coupled by separate wire branches that connect each load directly to the terminals of the power source (see Figure 2). Since each load is connected directly between the terminals of the power supply, the voltage drop through each load will equal the total voltage from the power supply. The current that travels through each load varies with the resistance of the load. The current in a parallel circuit can travel through multiple pathways. As a result, the arrangement of the loads allows the current to travel more efficiently, and thereby decreases the effective resistance of the entire parallel circuit. Since the effective resistance is lower, the total current is greater in a parallel circuit than in a series circuit with the same power source and load. Many circuits are controlled by a switch to turn a load on and off. All switches must have at least one terminal where the current enters (input) and a second terminal where the current exits (output). A switch that controls just one circuit is called a single pole (SP) switch. A single pole switch is commonly either single throw (ST) or double throw (DT). An SPST switch controls one circuit with a simple on/off switch. Closing the switch completes the circuit and the current flows. See Table 1 for how an open and a closed SPST switch is represented in a circuit diagram.

An SPDT switch has three terminals—one input or common terminal and two output terminals, often labeled A and B. When the switch is connected to one output terminal, current flows through that terminal but not through the other. When the switch is moved to the second output terminal, current no longer flows through the first terminal, but now flows through the second (see Figure 3). Understanding electrical circuits and how to apply this knowledge to solve related problems require both science and engineering practices. Scientists ask questions about natural phenomena and conduct investigations to find the answer to the question. Engineers define problems related to human needs and wants and design the best solution among many possible outcomes. Often the problem has particular criteria (requirements) and constraints (limitations) that influence the solution choice.

Experiment Overview

Explore electricity the STEM way! Learn about how electric circuits work while engaging in science and engineering practices. In the introductory activity, two bulbs will be connected in a series and then a parallel circuit. Another circuit will be made with a bulb that can be turned on an off by a switch. The procedure provides a model for designing and building more challenging circuits.

Materials

Prelab Questions

1. Examine the circuit diagram in Figure 4.
   {14072_PreLab_Figure_4}
   1. List the components that make up the circuit.
   2. Which type of circuit is represented in the diagram, open or closed?
2. For each statement the follows, indicate whether a series or parallel circuit is described.
   1. The current has only one pathway to flow from a battery, through two bulbs and back to the battery.
   2. The current has multiple pathways through which it can travel.
   3. Two bulbs of equal resistance are connected in a circuit to a 6-V battery. The voltage drop across each bulb is 6 volts.
   4. Two bulbs of equal resistance are connected in a circuit to a 6-V battery. The voltage drop across each bulb is 3 volts.
3. Examine the circuit drawings and diagrams in Figures 1 and 2.
   1. How are the drawings and the diagrams alike?
   2. How are they different?

Safety Precautions

Do not directly connect the positive and negative battery terminals without a load in between. The battery can discharge quickly and the terminals and alligator clips can become very hot. Please follow all laboratory safety guidelines.

Procedure

Note: Throughout all procedures, as soon as a successful circuit is built, disconnect the power source. This will help prolong the life of the bulbs and the batteries. Do not connect one bulb alone with two batteries. The bulb will receive too much current and burn out.

Part A. Two Lightbulbs in Series and in Parallel Circuits

1. Screw one lightbulb into a socket. Repeat with a second bulb and socket.
2. Using two batteries connected and three connector cords, make a complete circuit to the lightbulbs, using the circuit diagram in Figure 1 from the Background as a guide.
3. Note the brightness of the two bulbs in the series circuit and record your observations for Part A on the Introduction to STEM with Electricity worksheet.
4. Test the series circuit by removing one bulb from its socket. Both bulbs should go out.
5. Screw the bulb back into the socket and disconnect one terminal of the battery.
6. Refer to the circuit diagram shown in Figures 5a and 5b.
   {14072_Procedure_Figure_5_Two lightbulbs in parallel}
7. Connect six connector cords, two lightbulbs, two batteries, and two couplers together according to Figure 6. Caution: Make sure each alligator clip is connected to only one side of the paper clip coupler and the alligator clips are not touching each other. If they do touch, a short circuit may result. With a short circuit, the path of the current is shortened, resulting in less resistance in the circuit. Less resistance results in more current flowing through the circuit than was intended. This can cause damage to the circuit from overheating.
8. To test if you created a parallel circuit correctly, unscrew one lamp from its socket until the bulb goes out. The remaining bulb should stay lit. Test the other bulb in the same manner.
9. Observe the brightness of the two bulbs in the parallel circuit compared to the two bulbs in the series circuit. Record your observations on the worksheet.
10. Disconnect all the circuit components.

Part B. Make a Single Pole, Single Throw (SPST) Switch

1. Cut an index card in half. Set aside one half for Part C.
2. 2. Place a large paper clip in the center of the half card.
3. 3. Make a mark on the paper just inside one end of the paper clip (see Figure 6).
   {14072_Procedure_Figure_6}
4. 4. Repeat step 3 at the other end of the paper clip.
5. 5. Make a small hole at each mark with the tip of the longer prong of a paper fastner.
6. 6. Push both prongs of the paper fastener through one hole. On the underside of the card, spread the prongs apart so they lay flat against the card. Repeat with another fastener through the other hole.
7. 7. Slip the smaller end of the paper clip between the head of the fastener and the card. Swivel the paper clip around until the other end touches the second fastener (see Figure 7). This is a single pole, single throw (SPST) switch.
   {14072_Procedure_Figure_7}
8. 8. Test your switch by placing it in a series circuit with one battery and one bulb. Attach the alligator clips to one of the prongs of each fastener on the underside of the card.
9. 9. One you are able to turn the bulb on and off by rotating the paper clip, disconnect the battery and draw a circuit diagram for Part B on the worksheet.

Part C. Make a Single Pole, Double Throw (SPDT) Switch

1. Obtain the other half of the index card.
2. Make another single pole single throw switch as in Part B.
3. Make sure the smaller end of the paper clip is attached to a fastener, then rotate the other end of the paper clip so it is about half way between the second fastener and the bottom edge of the card (see Figure 8).
   {14072_Procedure_Figure_8}
4. Make a mark just inside the free end of the paper clip and push the prongs of another fastener through the mark. Spread the prongs flat against the underside of the car.
5. You now have a single pole, double throw switch.
6. Test the switch with the two batteries, one bulb and a coupler. Hint: One connector cord should connect one prong of the double throw switch to a coupler. A second connector cord should connect a prong of the other throw to the same coupler. Caution: Make sure the prongs of the two throws are not creating a short circuit by touching each other on the underside of the card (see step 7 of Part A).
7. If the circuit is wired correctly, the bulb should light when the free end of the paper clip switch touches either fastener head, and the bulb should go out when the paper clip switch is in between the two fastener heads.
8. Once you have built the circuit correctly, draw a circuit diagram for Part C on the worksheet.

Part D. Design Challenge

Read and follow the instructions for the challenge assigned by your teacher.

Challenge 1

A homeowner wants a dual electric outlet (two sockets) added to a room. One outlet will have a lamp plugged into it that will be turned on and off by a wall switch. The other outlet will have an alarm clock plugged into it that should remain on at all times, even when the lamp is turned off by the switch.

Additional Design Criteria and Constraints

• A bulb in a socket will represent the lamp and a second bulb will represent the lighted display of the alarm clock.
• A total of 3 V is to be used as the power source, which will represent the dual outlet. If using 1.5-V batteries, then two batteries combined will represent the dual outlet. The two batteries are considered one power source with one positive and one negative terminal.
• Only one alligator clip may be attached to the positive terminal and one clip to the negative terminal of the power supply.
• A maximum of six connector cords may be used.

Challenge 2

A homeowner wants a two-way switch to control a single light that is installed at the bottom of a set of stairs. One switch will be at the top of the stairs and a second switch at the bottom. Both switches control the one light. If the light is off, flipping either switch will turn it on. If the light is on, flipping either switch will turn it off.

Additional Design Criteria and Constraints

• A bulb in a socket will represent the light at the bottom of the stairs.
• A total of 3 V is to be used as the power source. If using 1.5-V batteries, then two batteries combined are considered one power source with one positive and one negative terminal.
• Only one alligator clip may be attached to the positive terminal and one clip to the negative terminal of the power supply.
• A maximum of six connector cords may be used.

Engineering Design and Procedure for Either Challenge

Form a working group with other students and discuss the following questions. Reflect on Figure 9 for the process involved in engineering.

1. Consider the challenge assigned to your group. What is the problem you are designing a solution for?
2. Consider the circuit models built in parts A, B and C. a. What type of circuit will the challenge require? b. What type of switch(es) will the challenge require? c. Will any couplers be needed?
3. Brainstorm possible solutions to the challenge with your group. On a separate sheet of paper, draw circuit diagrams to represent your possible solutions.
4. Choose the solution you believe will achieve the goal for the design challenge for Part C on the worksheet.
5. Obtain the necessary materials and build the circuit according to your choice. Test and evaluate the circuit.
6. If the solution does not work, repeat steps 4–5. If it does, draw the circuit diagram on a clean sheet of paper and attach it to the worksheet.

Student Worksheet PDF

14072_Student1.pdf