Fourth Grade - Science - Lesson 37 - Electricity
Electroscope activity adapted from The Ben Franklin Book of Easy Incredible Experiments by staff of the Franklin Institute Science Museum.

Objectives
Identify the charges of objects that gain extra electrons through friction.
Describe behavior of similarly charged and oppositely-charged objects.
Build an electroscope and test for the presence of static electricity.

Materials
Picture for transparency
For each pair of students: two balloons, a piece of thread, a plastic ruler, piece of cloth (wool works best), strip of aluminum foil, 1 by 4-inch piece of corrugated cardboard, metal paper clip, tissue paper, scissors, crayons, Investigating Static Electricity worksheet

Suggested Books
Berger, Melvin. All About Electricity. New York: Scholastic, 1995.
Cole, Joanna. The Magic School Bus and the Electric Field Trip. New York: Scholastic, 1997. Includes information on power stations and blackouts.
Epstein, Sam and Beryl. The First Book of Electricity. New York: Franklin Watts, 1977. Chapter 8 includes a section on static electricity as well as information about Thales and Ben Franklin's experiments with static electricity.
Franklin Institute Science Museum. The Ben Franklin Book of Easy Incredible Experiments. New York: John Wiley, 1995. Pages 50 through 55 contain fun "magic feats" with static electricity such as the electric leg spider and the moths in motion.
Markle, Sandra. Weather, Electricity, Environmental Investigations. Santa Barbara, CA: Learning Works, 1982. Pages 45 through 47 include projects and information on electrical charge and Thales.
Parsons, Alexandra. Make It Work! Electricity. New York: Scholastic, 1992. Pages 6 and 7 contain appealing illustrations of static electricity investigations.
VanCleave, Janice. Electricity: Mind-Boggling Experiments You Can Turn into Science Fair Projects. New York: John Wiley, 1994. Includes "How does matter become electrically charged?" plus 19 other experiments.
Whyman, Kathryn. Sparks to Power Stations. New York: Gloucester, 1989. Includes excellent diagrams showing how charges build up in a cloud as well as an interesting sidebar about using static electricity to remove dirt and soot from smokestack emissions.

Procedure
Ask the students if, when unloading clothes from a dryer, they have noticed that sometimes the clothes stick to each other and crackle when they are pulled apart. Ask if they have ever walked across a carpet, touched a doorknob and experienced a slight electric shock. Tell the students that in both instances they were experiencing the power of electrons in something called static electricity. Write this on the board. Remind the students that electrons are particles that circle the nucleus of an atom. Ask: Are electrons positively or negatively charged? (negatively charged) Ask: What are the names of the two particles that make up the nucleus of an atom? (proton and neutron) Are they positively or negatively charged? (positively charged) Tell the students that atoms hold tightly to the particles in the nucleus -- the protons and neutrons -- but electrons are loosely held. They move around from atom to atom easily. Tell the students that by tumbling together in the dryer, electrons from some of the clothing rub off onto other clothing. Show the students the transparency. Point out that by rubbing together in the dryer, a sock may pick up extra electrons from a shirt. Ask: What do you think happens to the charge of the sock when it picks up extra electrons? (The sock builds up a negative charge.) What do you think happens to the charge of the shirt when it loses electrons to the sock. (The shirt becomes positively charged.) Remind the students that positive and negative are attracted to each other. Ask: What do you think might happen to the positively charged shirt and the negatively charged sock in the dryer? (They would be attracted to each other and stick together.) What do you think happens when there are two objects with like charges such as two negatively charged objects or two positively charged objects? Are they attracted to one another? (No, like charges repel each other.)
Tell the students that 2,500 years ago a Greek mathematician and astronomer named Thales (TAY-less) first noticed the effects of static electricity. He was polishing a piece of amber. Ask: What is amber? (hardened sap or tree resin that looks like yellow stone) Tell the students that Thales discovered after he rubbed the amber that it attracted dust particles. Ask: Knowing what you do about static electricity, why do you think dust stuck to the amber? (Loose electrons were rubbed off the amber so it became positively charged. Negatively charged dust particles were attracted to the amber.) Tell the students that the Greeks' word for amber was elecktron. This is where we get our word electricity.
Ask: Have you ever taken off a sweater in the dark and seen sparks? (Accept all answers.) Tell the students that what they are seeing is the discharging of built up electrons. The flashes of light are caused by electrons flowing away. Point out that when walking across a fuzzy carpet, a person picks up extra electrons rubbed from the carpet and builds up a negative charge. When the person touches a doorknob, suddenly, the extra electrons that have built up are discharged -- flow away -- causing a tiny spark and a small electric shock.
Remind the students that when they studied weather they learned about a gigantic display of static electricity. Ask: What do we call this static electricity display that often happens during thunderstorms? (lightning) Point out the cloud diagram on the transparency. Remind the students that electrical charge is built up inside a cloud when ice particles bump into each other. This causes electrons to be rubbed off atoms and attach to others. The negatively charged atoms, the ones with more electrons, collect at the bottom of the cloud. The bottom of the cloud becomes negatively charged. Meanwhile the lighter atoms with fewer electrons rise to the top of the cloud. Ask: What do you think the charge at the top of the cloud would be? (positive) Tell the students that the charges build up until there is a sudden discharge of electrons -- a flash of lightning.

Tell the students that another name for rubbing together is friction. Write this on the board. Have two volunteers come to the front of the room. Give each volunteer a blown-up and tied balloon. Ask them to use friction to build up negative charges on the surface of their balloons. If they do not discover it right away, suggest they rub the balloon on their clothing. Point out that electrons from their clothing are now on the surface of the balloon. Ask: Is the balloon with extra electrons now negatively or positively charged? (negatively charged) The volunteers' clothing, now that it has lost electrons to the balloon, is it positively or negatively charged? (positively charged) Ask: What do you notice about the balloons and the clothing now that they have opposite charges? (The balloons stick to the clothing.) Point out that the opposite charges are attracted to each other. Tie a balloon to each end of a thread. Hang the thread over a ruler so the balloons dangle near each other. Point out that both the balloons are negatively charged. Ask: Are they attracted to each other? (no) Do they move away from each other? (yes) Why do you think they move away from each other? (They have the same charge so they repel each other.) Tell the students that objects do not remain positively or negatively charged. When extra electrons are discharged, an object goes back to a neutral charge. Protons and electrons are back in balance.
Tell them that with partners they will have a chance to try this investigation into friction and static electricity as well as try to solve the mystery of the jumping bugs. Group the students in pairs and distribute materials and investigation worksheets.

Possible Homework
Have the students list things at school and at home that require electricity to work or write an account of a citywide power failure or blackout and describe how they would cope without electricity.

Investigating Static Electricity

I. Try the balloon investigation yourselves.
Blow up and tie closed two balloons.
Rub them on your clothing or with the cloth.
1. Now that the balloons have picked up extra electrons, what is their charge, (+) or (-) ? _________
2. Describe what happens when a charged balloon gets close to an object with the opposite charge.

__________________________________________________________________

3. Tie the balloons to the thread and hang them on the ruler. Describe what happens when two objects with the same charge get close to each other.

________________________________________________________________________

________________________________________________________________________

II. Build an electroscope to test for static electricity:
Bend a paper clip into a hook shape.
Poke the straight end of the paper clip
between the layers of the cardboard.
Fold a two-inch wide strip of aluminum foil in half.
Loop it over the hook so the two ends of the foil hang down.
Rub one of the balloons and plastic ruler with the cloth
so they become charged.
1. Holding the electroscope by the cardboard, move it near the charged objects. How does the electroscope indicate that there is a charged object nearby?

__________________________________________________________________

III. Lightning bugs
Draw six one-inch bugs on tissue paper and cut them out. Place them on the desk.
Rub the plastic ruler with the cloth. Pass the ruler over the bugs.
1. Describe what happens to the bugs when the ruler comes near them.

________________________________________________________________________

2. Explain why you think this might happen.

________________________________________________________________________

Fourth Grade - Science - Lesson 38 - Electricity
Pass-the-Electron game adapted from The First Book of Electricity by Sam and Beryl Epstein.

Objectives
Demonstrate how electrons flow in a current.
Design, build and test a simple electric circuit.
Compare designs and identify uninterrupted flow of electrons as the important factor in a circuit.

Materials
Pennies, paper clips or some other tokens, one for each student, plus one extra
For each group of four students: a D cell battery, two 8" pieces of insulated wire with the ends stripped, electrical tape, a threaded flashlight bulb

Suggested Books
Epstein, Sam and Beryl. The First Book of Electricity. New York: Franklin Watts, 1977.
Glover, David. Batteries, Bulbs and Wires. New York: Kingfisher, 1995.
Parker, Steve. Electricity. New York: Dorling Kindersley, 1992. This Eyewitness series book includes information on discoveries about electricity, but its strength is its illustrations of dry cells, light bulbs and circuits.
Zubrowski, Bernie. Blinkers and Buzzers: Building and Experimenting with Electricity and Magnetism. New York: Morrow, 1991. This Boston Children's Museum Activity book contains clearly illustrated experiments.

Teacher Note
Suitable copper wire, called hook-up or lead wire, is available at any hardware store. After it is cut into lengths, at least one inch of insulation on the tips of each piece should be stripped off with scissors or wire strippers. In the other lessons prepared wire means that wire has been stripped in this way. Threaded bulbs are specified because holders for these bulbs will be required in the next lesson.

Procedure
Remind the students that last lesson they produced static electricity. Ask: What is static electricity? (build up of electrical charge) How did you produce an electrical charge? (by friction) Ask the students to give three examples of evidence of static electricity (clothes sticking together in the dryer, balloons sticking to clothes, lightning, sparks when taking off a sweater, a shock when touching a doorknob after walking across a carpet) Remind the students that the shock they might feel when touching a doorknob is the discharge of electrons. The extra electrons picked up from friction with the carpet move to the doorknob. For one split second, an electric current goes from hand to doorknob.
Tell the students that an electric current is a flow of electrons. Write electric current=flow of electrons on the board. This flow of electrons or electric current is energy. Show the students a length of copper wire and tell them that electric current can flow through wire like this. Have the students stand up so they might illustrate the flow of electrons through copper wire in a game called "Pass-the-Electron." Ask the students to arrange themselves in a line or several lines to represent the wire. Say: Each of you is an atom of copper in a length of copper wire. Give each student a token, such as a penny, marble, popsicle stick, etc., to represent an electron. Tell the students that each atom has the same number of electrons -- that number cannot be changed. If an extra electron is added to the first atom at the end of the wire, it must push an electron away. That electron jumps to the next atom.
Tell the students that you are the starter. As the starter, you give a token to the first person in each line. This token is an extra electron. Tell this first atom that he or she cannot have two electrons. He or she must push the extra electron off to the next atom. Have the student pass a token. Tell the next student in line that he or she now has too many electrons and must push an extra electron off to the next atom, and so on. Point out that at the end of the line, the extra electron is discharged (dropped) and the electrical current stops.
Tell the students that they have just illustrated a flow of electrons -- an electric current. Ask: How could you arrange yourselves so that the flow of electrons does not end, so that the electrons are not discharged at the end of the line? (a circle) Have the students rearrange themselves in circles. As starter, give a token to one of the atoms in the circle. Have the students play Pass-the-Electron again, seeing how quickly they can make the flow of electrons move. Ask: What if there is a gap in the wire? Separate two atoms in a circle so the electron cannot be passed. Ask: What happens to the flow of electrons? (It stops.)
When the game is finished and the students are seated, tell them that another name for a circular journey like the one the electrons made in Pass-the-Electron is circuit (SIR-kit). Write this word on the board. Tell the students that as they illustrated, in order for a flow of electrons to keep moving, the electrons must travel in a loop or circuit. A circuit is the path electric current takes as it flows.
Show the students a D cell. Ask: Does anyone know what this is? (battery) Tell the students that it is also called a dry cell. Tell the students that energy stored in a battery serves as a starter -- it pushes electrons into the wire to get the flow of electrons started. Divide the class into groups of four students each and distribute D cells to each group. Ask the students to look carefully at the batteries and describe three things about them. (Possible answers might include: It has a knob or button on one end; the button end is marked with a (+); it is heavy; the two ends are metal) Have someone read the warning on the label aloud. Point out that there are chemicals in the battery that store energy. Point out that in tiny writing on the side it says, AD size, 1.5 volts. Tell the students that the amount of pressure or force a battery has to push electrons is measured in volts. Tell them that 1.5 volts is very little force. The number of volts from a wall socket is 120 volts. That is enough force to give a very bad electric shock and do injury to a person. Caution the students never to experiment with house current -- the current from wall sockets.
Distribute two pieces of wire to each group. Ask the students to describe two things about the wire. (Possible answers might include: There is a plastic or rubber skin around the copper wire; the copper wire inside is metal, brownish orange, shiny.) Point out that the copper wire inside contains the atoms that pass electrons and carry the current.
Distribute a bulb to each group. Ask the students to describe three things about the bulb. (Possible answers might include: It has a glass compartment and a metal end; there are two wires inside the glass sticking up; there is a bead holding the two wires; it has a metal button on the bottom just as the battery does.) Ask the students to look very closely inside the bulb. Ask them if they can see a very, very thin thread of wire connecting the two wires sticking up. Tell the students that when a bulb lights up, this thread of wire called a filament is what glows bright. The light bulb is a device that uses the flow of electrons to produce light.
Tell the students that as young electrical engineers, they have been given an assignment. The assignment is to use what they know about the flow of electrons and design an electrical circuit that will light up a light bulb. The circuit will contain a starter (battery), a device that uses electricity (a light bulb) and wire to carry the electric current. Ask the groups to first make a
diagram of a circuit they predict will work, showing the arrangement of wire, battery and bulb.
After designing the circuit on paper, tell the groups to build and test the circuit they designed and write a description of the results. Have groups share results with the class as well as special tips such as where on the bulb the contacts must be made and where on the battery. Point out that there is more than one way to arrange the bulb, battery and wire to make the circuit. In some circuits, for example, the button on the bottom of the bulb is in direct contact with the positive button on the battery. On others, a wire may connect the bulb and battery. Ask: In looking at the designs that succeed in lighting the bulb, what one thing do they all have in common? (The wires make good contacts with the battery and bulb and there are no interruptions in the circuit.) Point out that with no gaps between the battery, wires and bulb, the flow of electrons is uninterrupted. The electrons can move through the wires, light the bulb, and complete their circular journey or circuit. Ask: What happens when you disconnect one of the wires? (The light bulb goes out.) Why does the light go out? (because the flow of electrons is interrupted in the circuit)

Possible Speaker
Invite an electrician or electrical engineer to speak to the class about his or her job, what is most enjoyable about it and about electrical safety issues.

Fourth Grade - Science - Lesson 39 - Electricity

Objectives
Test a group of materials to find which are conductors and which are insulators.
Chart results of tests.

Materials
Two 8" pieces of string
For each group of four students: D cell (battery), D cell holder, flashlight bulb, bulb holder, two 8" pieces of prepared wire, objects to test such as aluminum foil, pencil, eraser, plastic pen top, toothpick, cork, paper clip, rock, rubber band, a marble, etc., data chart

Suggested Books
Gibson, Gary. Understanding Electricity. Brookfield, CT: Copper Beech, 1995.
Markle, Sandra. Weather, Electricity, Environmental Investigations. Santa Barbara, CA: Learning Works, 1982. On page 55 is a worksheet for testing conductors and insulators and illustrations of objects that one can include in the tests.
Parsons, Alexandra. Make It Work! Electricity. New York: Scholastic, 1992. Pages 8 and 9 contain information and set ups for testing different conductors and insulators. Page 22 has a short description of how Morse code was used and a complete alphabet of the code.
Peacock, Graham. Electricity. New York: Thomson Learning, 1994. Includes clearly written information on conductors and insulators as well as two projects.

Procedure
Write circuit on the board. Remind the students that last lesson they designed and built a simple circuit to light a light bulb. Ask: What can you tell me about the designs that successfully lit up the bulb? (They connected the bulb to the battery ends with wires so that the electric current could make a loop.) Ask: What happened when there was a gap in the loop? (The bulb would not light.) Remind the students that the copper atoms in the wire passed electrons very, very quickly to make the bulb light. Ask: Do you predict that if you had used string instead of copper wire the light bulb would have lighted? (no) Have two volunteers come to the front and assemble a simple circuit to light a light bulb as the students did in the last lesson. Then have the volunteers substitute string for wire. Ask: Was your prediction correct? (yes) Tell the students that electrons can move through a material that is a conductor. Write this word on the board. Conductors do not hold tightly to their electrons so the electrons can move easily through them. Other materials hold their electrons more tightly. Their electrons do not move easily. These materials are called insulators. Write this word on the board. Ask: Do you think string is a conductor or an insulator? (insulator) Why? (because electric current does not move through it) Point out that the first circuit the volunteers assembled contained both conductors and insulators. Ask the students to name a conductor in the circuit. (copper wire) Ask: What makes you think copper wire is a conductor? (because electric current moves through it) Ask: What do you think is an insulator in the first circuit the volunteers made? What does not allow electricity to pass through it? (the plastic skin on the outside of the wire) What is the skin made of? (plastic) Would you predict that if I tested something else made of plastic, for instance, a plastic pen top, that it would be a conductor or an insulator? (insulator) Why do you predict that? (Because it is made of plastic; plastic is a material that is an insulator.)
Say: Suppose you have several different materials. How could you find out which materials are conductors and which are insulators? (Make a circuit and see if electricity will pass through them.) How will you know if electricity has passed through a material? (The light bulb will light because the electric current will be able to move around the whole circuit with no interruptions.) Point out that the circuits they built last lesson had a starter (a battery), a conductor (the copper wire) and a device that uses electricity (the light bulb). Ask them to build a simple circuit again and make sure the light bulb lights up. Then make a gap in the circuit, for example, where wire touches the battery. By bridging the gap in the circuit with different objects, they can find out if the materials in the objects are conductors or insulators.
Point out that it takes several pairs of hands to keep all the parts of the circuit touching. Show the students a D cell holder and a bulb holder. Tell them that using this additional equipment is not necessary to make a circuit, but the battery holder and the bulb holder can help secure the contact points. Show the students how the battery fits into the holder and how wires can be attached to the metal clips at each end. Show them how the bulb can be screwed into the bulb holder and contact made using the two metal clips or screws as contact points.
Divide the class into groups of four students each and distribute materials and data sheets for the insulator or conductor tests. Encourage the students to test other objects in the classroom and add the results of those tests to their data charts. When the students are finished recording data from the tests, compile the results in a chart on the board. Ask: What objects proved to be conductors? (aluminum foil, key, paper clip) What do these objects have in common? (They are all made of metal.) Point out that copper is also a metal. What does this tell you about metals? (Electric current can move through metals. Atoms of metal do not hold electrons tightly.) Which objects proved to be insulators? (pencil, eraser, rock, plastic pen top, toothpick, cork) Look at the materials these objects are made of. Which materials are insulators? (wood, rock, plastic, glass, cork)
Point out that when the students bridged the gap in the circuit with a conductor, such as a paper clip, the light went on. When it was removed, the light went off. The paper clip acted like an on/off switch for the light. Tell the students that next lesson they will experiment with different types of on/off switches.

Tests for Conductors and Insulators
Data Chart
 

Object

Material it is made of

Conductor

Insulator

 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

 
 

Fourth Grade - Science - Lesson 40 - Electricity
Build-a-telegraph activity was adapted from Make It Work! Electricity by Alexandra Parsons.

Objectives
Identify features of series and parallel circuits.
Describe how a switch works and construct two different types of switches.

Materials
For each group of four students for first activity: two D cells and D cell holders, four 8" lengths of prepared wire, electrical tape, two light bulbs and two light bulb holders, one 5" by 8" piece of corrugated cardboard for use as circuit base
Diagram of parallel and series circuits and switch for transparency
Flashlight that requires D cells
An assortment of switches
For each group of four students for additional activities: two metal thumbtacks, a metal paper clip, an 8 2" by 4" piece of lightweight cardboard, two 1" wide aluminum foil strips
Morse code sheet

Suggested Books
Franklin Institute Science Museum. The Ben Franklin Book of Easy Incredible Experiments. New York: John Wiley, 1995. Page 62 contains information on Morse code plus the entire code including letters, numbers and punctuation as it was when Samuel Morse invented it. It should be noted that the code has been modified since then.
Parsons, Alexandra. Make It Work! Electricity. New York: Scholastic, 1992. Pages 20 and 21 include directions for making three different kinds of switches.
Whyman, Kathryn. Sparks to Power Stations. New York: Gloucester, 1989. Contains excellent illustrations of parallel and series circuits on page 19 as well as of a two-way paper clip switch.

Teacher Note
A variety of switches -- toggle, pressure and knife styles -- is available at most hardware or electrical supply stores.
Remind the students that wires must be wound tightly around metal thumb tacks, paper clips, battery and bulb holder contacts. If the device does not work, they should check all contact points. Wires and bulb holders can be taped to a cardboard circuit base.
To be sure both types of circuits (series and parallel) are represented in the first activity, assemble a parallel circuit to have on hand.

Procedure
Divide the class into groups of four and distribute materials for the first activity. Remind the students that they used these materials -- battery, wire and a light bulb -- in the last two lessons to build a simple circuit. Tell them that this time the challenge is to assemble a circuit that lights up two light bulbs. Remind the students that the circuit must not have any interruptions. Suggest that they make a wiring diagram on paper and then assemble the circuit.

When the students are finished, show them the transparency of series and parallel circuits. Ask: Which kind of circuit did your group assemble: parallel or series? Point out that Christmas tree lights are often wired in a series circuit. Ask: What happens if you unscrew one of the light bulbs in a series circuit? Ask a group that has assembled a series circuit to unscrew one of the light bulbs and see what happens. (Both light bulbs go out.) Ask: Why did both bulbs go out when only one was unscrewed? (It made a gap in the circuit.) Ask: What else did you notice about the light bulbs in the series circuit? (They were dimmer than with only one bulb in the circuit.) Point out on the transparency that in a series circuit, current goes through one bulb and then the other. Ask: What do you think would happen to the brightness of these bulbs if you added another bulb to the series circuit? (All the bulbs would get dimmer.) Ask a group that has wired a parallel circuit to unscrew one of the bulbs. Ask: What happens to the other bulb? Does it go out? (No, it stays lit.) Why do you think the other bulb does not go out? (because the current can still flow through to it.) Point out on the transparency the path the electricity travels when one bulb is out. Ask: Are the bulbs dimmer in a parallel circuit? (No, they are both bright.) Tell the students that a parallel circuit draws more energy from the battery than a series circuit, so batteries do not last as long in a parallel circuit. Say: Suppose you were an electrical engineer working for BGE and your project was to design a wiring diagram for street lights in a neighborhood. Would you want the street lights to be wired in a series circuit or a parallel circuit? (parallel) Why? (because if one light bulb burned out, the other lights would stay lit; because each bulb would be bright) Would there be any advantage to wiring the street lights in a series? (They would draw less power; would require half as much wire)
Show the students a flashlight. Open the flashlight and show the students that two or more "D" cells are stacked inside and light one bulb. Point out that these batteries are lined up end to end in a series circuit to provide more voltage. Write 1.5 volts + 1.5 volts on the board. Ask: How many volts does a flashlight with two D cells provide? (3 volts) How many volts would a flashlight provide that had three 1.5-volt batteries? (4.5 volts) Say: Suppose you had one flashlight with two batteries stacked end to end in a series circuit. Suppose you had another flashlight with two batteries side by side and connected in a parallel circuit. In which flashlight would you expect the batteries to last longer? (stacked in a series because a parallel circuit draws more energy)
Turn the flashlight on and off several times. Ask: What am I using to turn the flashlight on and off? (a switch) Remind the students that last lesson they learned about materials that are conductors and materials that are insulators. Ask: When you were testing materials during the last lesson, how did you know if a material was a conductor? (The light went on. Electric current moved through the conductor and the circuit had no gaps.) Ask the students to name a material that is a conductor. (metal) Show the students a variety of switches that use conductors to bridge the gap in a circuit and then interrupt it. Tell the students that on/off switches on lamps, T.V.s, toasters, vacuum cleaners and other appliances work the same way. Ask: What happens to the circuit in an appliance when I flip a switch to on? (A conductor bridges the gap in a circuit and allows electricity to flow.) What happens when I flip it to off? (The conductor is moved out of the pathway of electricity and the flow stops.) Tell the students that two metal thumbtacks and a metal paper clip can be used to make a switch on the circuits they have built. Show the students the diagram of a paper clip switch on the transparency. Have a volunteer use the diagram to describe how the paper clip switch would work. Distribute paper clips and thumbtacks to groups and ask them to remove one light bulb and holder and build paper clip switches into their circuits.

When the students have finished incorporating paper clip switches, ask: Have you ever signaled a friend using a switch? (Accept all answers.) Point out that a light switch can be clicked on and off quickly to blink a signal. Remind the students that a doorbell or buzzer is also a device with a switch called a pressure switch. Ask: What do you think happens when you push or put pressure on a doorbell button? (A conductor connects to make an electric circuit complete and the bell or buzzer works.) Tell the students that they can make a simple pressure switch using one of the materials they tested in the last lesson. Ask: According to the results of your tests, was aluminum foil a conductor? (yes) Show the students two strips of aluminum foil wrapped and taped around the ends of a 4" by 82" piece of lightweight cardboard. Fold the cardboard in half so that the aluminum foil strips touch. Ask: What do you predict would happen if you taped the ends of two wires in your circuits to these two pieces of aluminum foil and then you did this? Would the aluminum foil complete the circuit? (Accept all answers.) Ask the students to see if their predictions were correct. Distribute cardboard and aluminum foil strips to each group to replace the paper clip switch. When the groups have wired in the pressure switches and they are operational, ask the students if they can switch the light bulbs on and off quickly. Tell the students that you are trying to design a device that will light up a light inside your house when someone comes to your door. Ask: How could a pressure switch like this one be used in that device? (The pressure switch could be placed under the doormat so the pressure of a person's feet would bring the aluminum foil together and light the light bulb. It also might be installed on the door frame like a doorbell button.)
Tell the students that more than 150 years ago a device for sending coded signals was invented that used a pressure switch called a tapper switch. The device was called a telegraph. Tell the students that next lesson they will build a tapper switch and send messages in a special code called Morse code.

Possible Homework
Have the students do research to find out about Morse code. Distribute the Morse code sheet and ask them to bring in a short message written in Morse code that they will send to a classmate by telegraph in the next lesson.

Morse Code

Morse code is made up of long and short signals. A dot is transmitted by a short tap or flash of light. A dash is transmitted as a long tap or flash. To say "boy" in Morse code, a code tapper would hit a telegraph key this way:
B long-short-short-short
O long-long-long
Y long-short-long-long.

Fourth Grade - Science - Lesson 41 - Electricity

Objectives
Interpret a circuit diagram and label its parts.
Build a tapper switch and send a Morse code message.

Materials
For each group of four students: two metal paper clips, D cell with D cell holder, light bulb and light bulb holder, electrical tape, corrugated cardboard 6" by 6" for tapper switch, corrugated cardboard 8" by 12" for a circuit base, three 10" lengths of prepared wire, one 36" length of prepared wire, paper and pencil, Morse code sheet from previous lesson, directions and wiring diagram (attached)

Suggested Books
Ardley, Neil. The Science Book of Electricity. San Diego: Harcourt, 1991.
Jennings, Tony. Electricity and Magnetism. Austin, TX: Steck-Vaughn, 1996.
Markle, Sandra. Weather, Electricity, Environmental Investigations. Santa Barbara, CA: Learning Works, 1982. Page 66 includes information on Morse code and building a telegraph.
Parsons, Alexandra. Make It Work! Electricity. New York: Scholastic, 1992. Pages 22 and 23 include brightly illustrated directions for building a telegraph set.
Snedden, Robert. The History of Electricity. New York: Thomson Learning, 1995.

Background Information
Samuel Morse was an American inventor who in the 1830s designed the first telegraph. His telegraph was a tapper switch called a Morse key and a printer. The switch allowed electricity to flow through wires to another key and printer. Each pulse that was received caused an electromagnet to move on an inked wheel so that it made a mark on a paper strip. For the first time messages could be sent long distances through wires. A message sent from New York could be received in San Francisco in less than a second. The code Morse devised is one of short and long taps on the tapper switch. Each letter in the alphabet is assigned an arrangement of taps. One Morse code message that is still understood by many people today is the distress signal, SOS: dot-dot-dot, dash-dash-dash, dot-dot-dot or as those who use Morse code would say: dit-dit-dit, dah-dah-dah, dit-dit-dit.

Procedure
Remind the students that last lesson they built two kinds of switches for a circuit. Ask: What kind of switches were they? (paper clip on/off switch and an aluminum foil pressure switch) Tell them that this lesson they will be building a different kind of pressure switch called a tapper switch and sending messages in Morse code. Ask the students to share information they uncovered on Morse code. Discuss the long time use of SOS as a distress signal and have students write it out on a sheet of paper in Morse code.
Divide the students into groups of four and distribute materials plus the wiring diagram sheets. Ask the students to look at the diagram of the tapper switch. Ask: What conductors come in contact to complete the circuit on this pressure switch? (paper clips) Tell the students to be sure when assembling the switches to align the paper clips so they will touch when the cardboard is folded over. Point out that tape can be helpful to hold wires in place.

Tell the students that when they have finished assembling tapper switches and circuits, they will be connecting their circuit to that of another group according to the diagram. Point out that the wires connecting their tapper switches to another group's could be very, very long. The other group could be in another part of the building or another part of the country. With enough volts of electricity provided by a starter, the signal could travel along wires from Baltimore to the tip of South America.
When the circuits are assembled and connected, have students practice short and long taps by sending the SOS distress signal. When they are comfortable discriminating between long and short signals, encourage groups to send Morse code messages of a few words. Suggest that the groups receiving the message write down the signals as dots and dashes and then decode them. Perhaps the message might be a question that the other group can answer such as "Do you like spinach?" or "Who is your favorite singer?"
When the students have had a chance to send and receive Morse code messages, tell them that you have a challenging question to ask them about the circuits they have built. Ask: Are the two bulbs wired in a series circuit or a parallel circuit? Suggest that one way to find out is to unscrew one of the bulbs. Ask: How would unscrewing one of the bulbs in the circuit help us decide whether this is a series or parallel circuit? (If it is a series circuit, unscrewing a bulb will make the other one go out. If it is a parallel circuit, the other bulb will remain lit when the switch is on.) Have the students try unscrewing a bulb in the circuit. Ask: Is it a parallel or series circuit? (parallel) Ask the students to label the wiring diagram using these labels: starter, switch, conductor, and device that uses electricity. Write the labels on the board.

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