Unit 1: Energy Basics - Washoe County School District€¦ · The activity requires some knowledge construction. R W -1 . The activity’s primary purpose is problem solving. L e

Unit 1: Energy Basics Lesson 2: Series & Parallel Circuits (Optional - Not Tested)

Adapted from: Magnetism and Electricity FOSS kit (grades 3-4), Investigation 3 Grade Level: 7-12 Time: 40-60 minutes Updated July, 2017

Science Standards For a full description of each standard see the Unit Overview.

Next Generation Science Standards (NGSS) High School HS-PS2-5. Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.

Next Generation Science Standards (NGSS) Middle School MS-PS2-3. Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.

MS-ETS1-2. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

21st Century Competencies

C-1. Students are required to work in pairs or groups.

KC-1. The activity requires some knowledge construction.

RW-1. The activity’s primary purpose is problem solving.

Lesson Objective

● The students will construct series and parallel circuits to explore ways to operate more than one component at a time in a circuit and demonstrate evidence of the flow of electricity through a light bulb.

Essential Questions

● Can multiple receivers be powered in a single circuit? ● How can single circuits power multiple receivers at the same power level?

Concepts

● Series circuit, parallel circuit.

Adaptations for ELL, Special Ed, or G.T.: ● Gifted Students: Generate questions

■ What other circuits, using other components, that students could we set up? ■ Could you build a circuit that runs a motor and a light? ■ Could you build a circuit that runs a motor and two lights?

○ Timing permitting, give students a chance to build circuits that would answer the questions. Have them draw a diagram of each new circuit on the back of the student sheet.

Energy Basics - 1.2.1

Management Strategy: ● Organize the class into teams of 3-4 students and assign the following roles: GETTER (gets materials);

REPORTER (speaks for group when called upon); and STARTER (initiates the following of directions).

Background knowledge

Teacher: Comparing Series & Parallel Circuits Students will have worked with a Simple circuit - one source of electric energy connected to one energy receiver. When a conductive pathway is formed, say by a copper wire and connected motor, electric current flows throughout the circuit, and energy from the moving electrons transfers to the receiver. But what happens when two receivers are connected to one source? Or when two sources are applied to one receiver? Students grapple with these questions in this investigation. Series Circuits We have developed the operational definition of a circuit as a circle through which current flows from the negative (-) end of a battery to the positive (+) end of the battery, passing through a bulb along the way. But now we want to light two bulbs. The most intuitive solutions to the problem is to open the circuit, insert the second bulb, and close it again. Now the circuit is bigger, and the electric current will flow first through one bulb and then the other as it moves through the circuit. One source is now supplying two receivers. This is a series circuit. A series circuit has two or more components attached to a source in such a way that the current follows only one pathway through all the components, one after the other. If one component is disconnected from the circuit, current stops flowing to all the components in the circuit. Students will notice that two bulbs in series both produce light, but the light is not as bright as a single bulb connected to the source. Students often develop a model where the bulbs are sharing the electricity, so they are both dimmer than the one that gets all the electricity. This model is good for elementary school students. A better model is based on resistance. Some materials, like tungsten filaments, resist the flow of electrons by erecting, in effect, a bunch of roadblocks. The number of electrons making it through the resistive circuit at any given time decreases. The reduced flow accounts for the reduced intensity of light. But, because we will not be developing the concept of resistance, the concept of sharing electricity of resistance, the concept of sharing electricity we serve well.

Parallel Circuits Faced with the problem of getting two bulbs going, some students will get additional wires and connect the second bulb by adding a second loop of wires to the first circuit. Now both bulbs are shining as brightly as one bulb alone. This is a parallel circuit. A parallel circuit has two or more components, each with an equivalent pathway on a circuit. In our two- bulb example, both bulbs have their own pathway to the sources so no “ sharing” occurs. Both bulbs are bright.


The wiring of parallel circuit is a little more tricky than the wiring of series circuits. There is really only one way to construct a series circuit: adding components one after the other. You can change the order, but they all end up in one circle. Parallel circuits can look quite different from one another, but when you analyze them, they all are functionally the same. Here are six ways to hook up two bulbs that behave exactly the same. In every case the electricity “ leaves” the negative end of the battery, comes to a place where the flow has the option to take two paths, and eventually comes back together to return to the positive end of the terminals of the battery. In these first two designs the option to split happens right at the terminals of the battery.

In the other four wiring designs, the options to split happens at one side of the bulb.

In each example the current dynamics in the circuit are exactly the same. The brightness of the two bulbs in series and the two bulbs in parallel is visibly different. It seems logical that more energy is used for the parallel bulbs than for the series bulbs because more light is emitted. This is right. Two bulbs in parallel use electric energy twice as fast as one bulb. Consequently, the battery powering two light bulbs in parallel will go dead twice as fast as the battery powering one bulb. How does that compare to the two bulbs series? The two bulbs in series are very dim because they use electric energy even more slowly than one bulb, so the battery will last longest with two bulbs in series. Batteries in Series and Parallel So far we have considered components in series and parallel with only one battery. What happens if two or more batteries are put in series or parallel with each other? Basically, when you put two batteries in series, pointing the same direction (plus to minus), the voltages add up. Two 1.5 volt D-cells in series put out 3.0 volts. However, if two cells are put in series opposing one another, the voltage subtracts. Two D-cells will neutralize one another, putting out zero volts if they are oriented plus-to-plus or minus-to-minus. The orientation matters because current from a D-cell is direct current, which flows in only one direction. By our convention, electric current flows from the negative terminal (the flat end of a D-cell) to the positive terminal (the end with the bump). So, if two D-cells are oriented base-to-base or bump-to-bump, current attempts to flow, but in opposing directions. The electrons have, in effect, a head-on-collision, and flow stops. When two batteries are put in series, the voltage adds. As the voltage goes up, the current also goes up, so you get a much brighter light from the single bulb. In fact, you have to be careful about adding too many batteries in series because the current can soon exceed the limits of the filament, and it will burn up. However, when two batteries are put in parallel, there is no increase in the voltage - the bulb will burn with the same brightness as a bulb connected to a single battery - but the bulb will burn twice as long before you need to


change the batteries. So, if you want more energy, put your batteries in series. If you want the source to work longer, put the batteries in parallel. Switches in Circuits A switch is an excellent example of an intuitive component. When the switch is open, the circuit is broken, and no electricity flows. When the switch is closed, the circuit is complete, and the current flows. Occasionally however, students construct a circuit in which the switch works in reverse. As long as the switch is open, the bulb produces light, but as soon as the switch is closed, the light goes out. What’s that all about? What the students have done is to put a switch in parallel with the bulb. When the switch is open, the current has only one path to follow - the path through the bulb. The bulb lights. When the switch is closed, the current has a choice of two pathways - through the bulb and through the switch. When the current is offered two paths, one with a lot of resistance (the bulb) and one with virtually no resistance (the switch), essentially all of the current will flow through the switch. The bulb will immediately go out. Students sometimes call this the “reverse” switch,” one that turns the light on when the switch is opened, and turns the light off when the switch is closed. This kind of low-resistance conductor that bypasses a component is a short circuit. It can be dangerous if the circuit is carrying a lot of current, as in a typical house wiring, because the wires can get hot enough to start a fire. With D-cells there is no danger of fire - just the surprise of hot wires and the untimely exhaustion of the energy in the cell. The switch that students use in this activity is a single pole/single throw (SP/ST) switch. It is a simple on/off switch that usually opens and closes one simple circuit. A single pole/double throw switch can control two different circuits. A SP/ST switch can complete one circuit or the other circuit, or turn both off, but it cannot turn both circuits on at the same time. Look at the schematic. One throw of the switch handle closes the circuit with the bulb, and the other closes the circuit with the motor. This is an advanced switching circuit some students may be ready to tackle as a project.

Teaching Students About Electrical Circuits The fundamental notion of a circuit presented in this lesson is necessary before more complex circuitry can be understood. The most common model students use to add items to a circuit (such as lighting two bulbs or running a motor and lighting a bulb) is to chain or link them, one after another, in an increasingly larger circle or circuit. Students are challenged to add various combinations to the circuit and take careful note of what they observe (e.g. What happens to the brightness of bulbs when more bulbs are added, one by one? Is it possible to run a motor and light a bulb at the same time? What happens if more D-cells are added to a circuit?). Students generally obtain answers to the challenges by linking items in a series. To resolve advance challenges, students need to learn about parallel circuits. Students explore this circuitry with various combinations of items and compare results with the series circuits they tested earlier. By the end of this investigation, students should have extensive ideas about how to arrange components in circuits to accomplish certain purposes. Student:

● Life Experience – Students have experience operating circuits in their homes, personal appliances, and classrooms. Some students may have had science teachers who went through similar topics and activities as early as fourth grade, while this may be the first time investigating circuits for other students. Students understand that switches (like with classroom lights) turn things on or off. One good example of


series or parallel circuits is a set of holiday lights or bulbs on a string. If students have ever experienced a burnt bulb causing the whole line to not light up or a burnt bulb having no effect on the rest of the lightbulbs, they have seen an example of series or parallel circuits, respectively.

Materials List- Unit 1: Lesson 2: Activities 1-2

For each group: ❏ 1 Circuit base ❏ 1 D-cell, alkaline ❏ 1 Cell holder ❏ 1 Switch ❏ 2 Lightbulbs in holders ❏ 1 Electrical motor (optional)* ❏ 2 Long wires, 20-gauge, 30 cm ❏ 4 Short wires, 20-gauge, 15 cm

For the class: ❏ 1 Wire stripper

Handouts:

❏ Advanced Connections * ❏ Circuit Review sheet *

* Supplied by the teacher (use the duplication master to make copies of handouts).

Before Class:

➢ Wires should already be cut. Check to make sure that all the ends are stripped of insulation. If any ends are broken off, strip about 1 cm of insulation from the end that is broken off, using the wire stripper.

➢ Check D-cells. If you started with new D-cells, they should still be in good working condition and do not need to be checked. If you started with used cells, use a motor to make sure they are still in good working order. If the motor runs, the cell is usable.

➢ Put bulbs in holders. Put a bulb in each holder, ready for students to use. The bulbs and holders will last much longer if they are not constantly taken apart and put back together.

Safety procedures

● While rechargeable cells are not recommended for use with students because of the danger of rapid discharge in short circuits, the 1.5 volt D-cells included in the kit are very safe.

● Students should also often be reminded that, while it is safe to investigate with one 1.5-volt D-cell, wall sockets are dangerous and off limits as a power source for this investigation and in general (as household electricity is 110-120 volts).

● If students complain that the bulb or battery is getting hot, tell them to stop what they are doing and try something else. The heat is evidence of a short circuit.


Lesson Body

TTW= The Teacher Will (what the teacher should be doing) & TSW= The Student Will (what the student should be doing)

Engagement: ● TTW remind students of the simple circuits they worked on yesterday by drawing a schematic of a circuit

on the board that includes a bulb, a battery, and a switch in a circuit. TTW review the vocabulary associated with the schematic.

● TTW introduce the essential question(s) to the class:

■ How can you get two bulbs to light at the same time?

● TTW distribute the Advanced Connections sheet and ask students to draw in Box 1 a schematic diagram of a circuit they think will light two bulbs.

Exploration:

Activity 1: Series Circuits to Light Multiple Bulbs (25 minutes)

● When the students have drawn their schematic diagrams, ask GETTERS to get the materials the group will need to build the two-bulb circuits. The only circuit students can set up easily with three wires is a series circuit. Consequently the lightbulbs will be dim.

○ Materials needed: 1 circuit base, 1 D-cell, 2 bulbs in holders, 3 short wires, 1 switch.

Explanation: ● TTW Introduce Series Circuit

When students report that they got two bulbs glowing, but very dimly, tell them, ○ When two bulbs are connected in one big circuit, so that the electric current has to go through all

the components one at a time, that is a series circuit.

● TSW Generate Explanations for Dim Lights Give groups three minutes to discuss the following question:

■ Why do you think the lamps are dim in a series circuit?

● TSW Share Explanations for Dim Light Call on REPORTERs to offer group explanations for dim lights. TTW write ideas on the board or on a sheet of paper for future reference. They may suggest:

○ The battery is weak; Light bulbs have to share the electricity; Two bulbs slow down the electricity more than one; etc.

● Propose Solving the Low-Light Problem TTW tell students that these two lights in series are a problem. They are too dim to be of any use. Ask,

■ Can you make the two lights bright in your series circuit?


○ Materials needed: Tell students to pair up with another group so they have one additional D-cell, one additional cell holder, and an additional wire.

● Review Two Cells in Series TSW discover that when two D-cells are used in series the result is either two bright lights or no light at all (depending on orientation of D-cells)! TSW compare circuits to see if they can figure out the reason for these divergent observations.

★ Teacher Note: Students should not use more than two D-cells at a time. More will results in burnt-out

bulbs.

● Discuss D-Cell Orientation Students should conclude that the orientation of the D-cells is the determining factor. If both cells are pointing the same direction, the bulbs produce bright light. If the D-cells are pointing in opposite directions, the bulbs will not light. TTW ask students to describe what they figured out about D-cells in series. Important things for them to note include:

○ If the D-cells are pointing in opposite directions, the bulb does not light. ○ If the D-cells are pointing in the same direction, the bulbs shine more brightly than with only one

battery. ○ Electricity from D-cells flows only in one direction. If cells are pointing in opposite directions, the

electricity from one cell “runs into” electricity from the other cell, and the flow stops.

● Record Successful Circuits TSW return to their Advanced Connections sheets to draw in box 2 a schematic diagram of the circuit that they used to successfully light two bulbs brightly. They should label their diagrams “series circuit.”

Elaboration:

Activity 2: Building Parallel Circuits (25 minutes)

● TTW challenge students to build a different circuit using two bulbs: Last time you were able to light two bulbs with one battery, but the bulbs were so dim you could hardly see them. You put two cells in the series circuit, and that fixed the dim-light problem. But now here’s another challenge. Talk it over with your group, and when you have an idea, the GETTERs can get the materials you need to test it.

■ Can you light two bulbs brightly with just one battery?

★ Teacher Note: students should only be using one D-cell for this activity.

● TSW Build Circuits Encourage students to assemble, take apart, and reassemble the circuits as many ways as they can think of. The STARTERs should make certain that every student has a chance to assemble a parallel circuit. When students find a way to light both bulbs brightly with just one D-cell, have them draw a schematic of the circuit on their Advanced Connections sheet in box 3.

● TSW Share Results There are several ways that students may solve the challenge. Have a few students draw diagrams on the board. They usually discover design A, but may have come up with others.


● TTW Introduce Parallel Circuit

Acknowledge the circuits students have drawn on the board. Use one drawing to trace the path taken by the electricity from the cell to bulb 1 and back to the cell. Trace the path from the cell to and from bulb 2. Tell students,

○ The current leaving the cell has two pathways it can follow. It can go on this wire to bulb 1, and it can go on this other wire to bulb 2. Each bulb has its own pathway to the cell.

○ Whenever a circuit splits and goes to two or more components, that is a parallel circuit. The bulbs are said to be in parallel.

● TTW show all the possible schematic diagrams for parallel circuits. Trace one or two other parallel circuits

to show that the pathway always splits and goes to both bulbs, before coming back together to return to the battery.

● TSW draw all possibilities on their Advanced Connections sheet.

Advanced Circuit Challenges:

● As more schools implement Project ReCharge, more students will enter high school with basic circuit background knowledge. You can differentiate the lessons by pre-assessing background knowledge during the lightbulb and paperclip engagement then group students who are proficient in basic circuits into sub groups and provide them with additional challenges while students who are still developing their skills work through the series and parallel circuits.

● TTW: give different challenges to different groups based on background knowledge. ● TTW: Give the Advanced Connections handout to the students who are still developing their skills. For

students who need more challenge the Advanced Challenges handout. ● Teacher Note: Students who receive the Advanced Challenges handout will need additional materials:

additional wire, bulb holders, bulbs, switches and motors.

● TSW Generate a Class List of Questions Ask students to contribute to a list of questions or ideas for new and more complex circuit investigations. Some hints you might offer: What could you do with a switch? What could you do with another cell? Here are a few questions to add if they have not been said:

■ In a circuit with two bulbs in a parallel, where would you put a switch to turn just one bulb off? Where would you put the switch to turn both bulbs off?

■ If you are using design A, what do you do to add a third light bulb? ■ Would another D-cell affect the brightness of two bulbs connected in parallel? ■ How many bulbs in parallel can one D-cell light? (Several groups will have to work

together or maybe the whole class for this.)

● IF ADDITIONAL TIME IS AVAILABLE: Set up new investigations based on the class generated list of questions. Each group can choose a different question to answer and then report to the class. Students could record observations from these new investigations on the back of their Advanced Connections paper or on another sheet of paper. You may want them to write a sentence or two to explain their conclusions.


Evaluation: ● Formative: Qualitative Data

○ Revisit the essential question(s) ■ How can you get two bulbs to light at the same time? ■ How can you light two bulbs brightly with just one battery?

○ Assess Progress: Use these questions to reinforce concepts emphasized in the lesson: ■ What do we call a circuit in which all the components are connected in one big circle so

there is only one pathway for electricity to flow? [series circuit.] ■ Why do you think the lights are dim when only one battery is used? [Accept all

reasonable ideas. For example, components share the energy in a series circuit so the bulbs are dim.]

■ Is the orientation of the batteries important when you use two in a series circuit? [Yes, they must point in the same direction.]

■ How does electricity flow through a parallel circuit? [A parallel circuit provides a direct path for electricity to serve each component.]

■ Which circuit can run more components from one D-cell? Why is that so? [Many more components can be run from a single D-cell when the components are connected in parallel because each has a direct pathway to the source.]

● Summative: Quantitative Data

○ TSW answer a series of questions on the Circuits Review Sheet. This assessment can be completed during class or at home.

○ Discuss both types of circuits: ■ Use the Venn Diagram to compare and contrast series and parallel circuits. ■ Can you say when a series circuit might be the best design? When a parallel circuit might

be the best design?

Clean-up: ● Ask the GETTERS to collect all the materials and return them to their storage containers at the materials

station.

Closure: ● Relate the concept of series and parallel circuits to the circuits students encounter in their own lives. What

things in a house might run on series circuits? What things in a house might run on parallel circuits? Now that students have explored the different types of circuits, tomorrow will focus on materials that either help or slow down energy flow.

Vocabulary

❏ Series circuit: a circuit with only one pathway for current flow. ❏ Parallel circuit: a circuit that splits into two or more pathways before coming together at the source.


BLANK PAGE


Handouts for Unit 1: Energy Basics Lesson 2: Series & Parallel Circuits

Advanced Connections - Print one page, one-sided

Advanced Challenges- Print one page, one-sided (alternative assignment to challenge students)

Circuit Review Sheet - Print one page, one-sided


Name________________________ Date______________

Advanced Connections Directions: draw a schematic diagram when instructed.

1. I think I can light two bulbs with this circuit:

2. This is one way I made two bulbs light: This is a _______________ circuit.

3. This is how I made two bulbs shine brightly with one battery: This is a _______________ circuit.

Directions: Write the definitions for the following vocabulary words.

➔ Series Circuit: ___________________________________________________________________________________ ____________________________________________________________________________________

➔ Parallel Circuit: ___________________________________________________________________________________ ____________________________________________________________________________________

Possible Schematic Diagrams

A.

B. C.

D.

E. F.


Name________________________ Date______________

Advanced Challenges Directions: Each person in your group will draw a schematic (a drawing of a circuit) that includes all of the components listed and does the job described. Once each person has drawn their schematics. Share your drawings and discuss differences. Assign the building of one circuit to each person in the group. As a group, test your schematics to see if they work. When you have a working circuit, raise your hand to show your teacher and get it checked off. Continue building the circuits until each challenge is solved and signed off. Then as a group, decide on a new unique circuit, draw the schematic on the back of this handout and build it.

Parallel circuit, two lamps, one motor all controlled by a switch.

________Teacher’s approval

Parallel circuit, two lamps, one motor only the motor controlled by a switch.


Parallel circuit, two motors, one lamp. Only one motor controlled by a switch.


Two separate parallel circuits, two lamps controlled by one switch, one motor and one lamp controlled

by a second switch.



Name________________________ Date______________

Circuit Review Sheet Directions: Compare and contrast series circuits and parallel circuits on the Venn Diagram below.

Directions: Answer the following in complete sentences. 1. When might a series circuit be the best design?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

2. When might a parallel circuit be the best design?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

_________________________________________________________________________________________


Documents

Unit 1: Energy Basics - Washoe County School District€¦ · The activity requires some knowledge construction. R W -1 . The activity’s primary purpose is problem solving. L e