Electricity Experiments
Index Circuit Quiz Game
3
Conductors and Insulators
4
Connect the Circuit Game
5
Electric Currents and Magnetic Fields
7
Electroscope
8
Lemon Battery
9
Parallel and Series Circuits
11
Simple Circuits
12
Static Electricity
13
Supply List
15
References
16
Children’s Literature
17
Notes
18
Circuit Quiz Game
Index
A fun, versatile quiz game can easily be made using the concept of a complete simple circuit. The game board consists of a column of questions opposite a column of answers. If the correct match is made, a bright light bulb shows you have the right idea.
Materials
Cardstock 2 batteries 2 battery holders 4 alligator clips 1 flashlight bulb 1 bulb holder Aluminum foil Tape Plastic film
What To Do
Using an 8 by 11-inch piece of cardstock, punch five evenly spaced holes down the length of the page of an inch from the side. Do the same on the opposite side so that the holes line up with each other. Cut the plastic film into a 6 by 11-inch piece and use tape to secure it to the cardstock game board between the two sets of holes. On the film next to each hole on the left write a question or one half of a matching pair (suggestions include multiplication problems or state and capitals or anything else.) Next to the holes on the right side write the answers or remaining halves, but jumble the order so that questions correct answers are not directly across from them. Cut the aluminum foil into half-inch wide strips and stretch the strips shiny side down across the back of the game board to connect question holes with the appropriate answer holes. Use tape to secure the foil to the cardstock, but also to cover it completely to avoid any direct contact with other foil strips.Cover the back of the game board (the answer key) with another piece of cardstock and secure it with tape. Connect two batteries in series by snapping their holders together and connect one alligator clip to each end of this battery assembly. Connect the other end of one of the alligator clips to a light bulb in a holder and attach a second alligator clip to the other side of the bulb holder. There should be two alligator clips ends left and they are used to touch the foil-covered holes on the game board for a question and its answer. If the clips touch a question hole and the correct answer hole, the bulb will light! The game can be used to test anything from state capitals to multiplication tables because new questions and answers can be written on the plastic film. And the foil strips can be rearranged to keep the quiz-takers on their toes.
Question
1. Why does the bulb light up when the correct answer is chosen?
Source
“Power Up.” Sandra Markle, Atheneum: New York, 1989, p. 24. © S. Olesik, WOW Project, Ohio State University, 2001.
Conductors and Insulators
Index
Electricity flows into our homes through metal wires. What else can it flow through? Conductors are materials through which electricity can flow and insulators are materials through which it cannot. A variety of things found in the classroom or around the house can be tested for their ability to conduct electricity.
Materials
1 battery 1 battery holder 1 flashlight bulb 1 bulb holder 3 alligator clips Cardboard Metal thumbtacks or brads Coins Keys Cork Buttons Fabric Screws Marbles Plastic String
What To Do
Place the battery in the holder and attach an alligator clip to each of the leads on the battery holder. Connect the light bulb, in its holder, to one of the wires that is attached to thebattery. Connect another alligator clip to the other lead on the light bulb holder. Cut a piece of cardboard roughly 2 inches by 2 inches. In the center of the cardboard insert two metal thumbtacks or paper fasteners about an inch away from each other. Connect one of the remaining alligator clips, one leading from the battery and one leading from the light bulb, to each of the thumbtacks. An open circuit has been created, with the gap between the thumbtacks serving as the break in the circuit. Test various materials for their conducting ability by using them to bridge the gap between the thumbtacks. Conductors, such as coins, lying across the gap in contact with the thumbtacks should make the light bulb light. Insulators will not because they do not complete the circuit.
Questions
1. Why does the bulb light when some things are used to connect the tacks, but not others? 2. What materials made the bulb light? Could you guess which other materials would be conductors or insulators?
Source
“The Science Book of Electricity.” Neil Ardley, Harcourt Brace and Company: London, 1991, p. 20-21. “Science Experiments with Electricity.” Sally Nankivell-Aston and Dorothy Jackson, Franklin Watts: New York, 2000 p. 16-17. © S. Olesik, WOW Project, Ohio State University, 2001.
Connect the Circuit Game
Index
Electricity can flow though a complete, closed circuit, but cannot flow though an open circuit. This concept is reinforced with a fun game that tests the steadiness and patience of the players while illustrating this basic fact.
Materials
Bare wire or metal clothes hanger 1 flashlight bulb 1 bulb holder 2 batteries 2 battery holders Insulated wire Cardboard Tape Clay (if using the clothes hanger) Steel wool (if using the clothes hanger)
What To Do
If using bare wire, cut a piece approximately two feet long and wrap each end around one finger a three or four times to make a loose coil. Cut an 8 ďż˝ by 11 inch piece of cardboard. Attach the wire to the cardboard by taping each of the coils down to opposite ends of the cardboard sheet. The wire should stand up in sort of a U shape. Bend the wire so it looks like a wavy, squiggly line sticking up a few inches from the cardboard. If using a wire coat hanger, first use steel wool to remove any coating from the metal. Do this outside and avoid breathing the material that is being removed. Untwist the hanger and bend it into a U shape. Stick either end of the U into a lump of modeling clay, and then stand the U upside down with the clay as the base. Bend the hanger so it looks like a wavy, squiggly line. Connect the two batteries by clipping their holders together, and attach an alligator clip to each end of this battery pack. Attach one of the alligator clips to the wavy wire near the base of one side. Cut a six-inch piece of insulated wire and strip one end ďż˝ inch and the other 1- inch. Connect the shorter stripped end to the other alligator clip. The longer stripped end should be loosely wrapped around the wavy wire to form a loop. When the loop touches the wavy wire it completes the circuit and lights the bulb. The object of the game is to use the loop to trace the entire length of the wavy wire without touching them together and without completing the circuit. If the entire length of the wire can be traced without making the bulb light up then the game has been won!
Questions
1. Why does the light bulb light when the loop touches the wire? 2. Does the game still work with one battery instead of two? What difference would it make? 3. Can you think of any other games or toys that also use open and closed circuits to decide who wins and who loses? 4. Invent a new game that uses open and closed circuits. How would it work? 5. Would the game still work if the loop were made of insulated rather than bare wire? Why or why not?
Summary
The game is based on the fact that electricity flows through closed circuits, not open circuits. The circuit is open when the loop is not touching the wavy wire, so the bulb is not lit because no electricity is flowing through it. When the loop does touch the wavy wire, it completes the circuit, giving the electricity a continuous path to travel; the light bulb lights and the game is lost. The game requires good hand-eye coordination, and should help build an understanding of electrical circuits.
Source
“Awesome Experiments in Electricity and Magnetism.” Michael DiSpezio, Sterling Publishing Co.: New York, 1998, p. 94. “Edison Etc.” The Wild Goose Company: Salt Lake City, 1994, p. 60. © S. Olesik, WOW Project, Ohio State University, 2001.
Electric Currents and Magnetic Fields
Index
This activity provides an opportunity to see the effects of an induced magnetic field and to explore some of its properties.
Materials
10 yards of insulated copper wire Wire strippers Tape Thread Magnet Beverage can Battery
What To Do
Strip a few inches of both ends of the wire and wrap the length of wire around the can, leaving about a foot loose at each end. Then slide the coil off the can, being careful to keep the coil together. Wrap tape around the coil so it will keep its shape, then tape the coil to the table so that it will stand up. Magnetize the needle by rubbing it with the magnet. Stroke the needle with the same end of the magnet in the same direction at least forty times. Tie a piece of thread around the middle of the needle, then tape the other end of the thread to the inside of the top of the coil so the needle hangs in the middle. To illustrate the effect a magnetic field will have on the needle slowly bring the magnet near the needle, so that the needle still hangs freely, but points toward the magnet. Put the magnet away, but see the same effect on the needle by connecting the ends of the wire coil to the positive and negative terminals of a battery. The current flowing through the coil produces a magnetic field. Watch how the needle reacts.
Questions
1. What would happen if the wires were switched so that they touched the opposite terminals of the battery? Make a prediction, and then test it. 2. If two batteries were used instead of one, would the needle’s reaction to the current be different? 3. Does a non-magnetized needle work? 4. Ten yards of wire is quite a bit. Would a significantly shorter length of wire work? How might it change the experiment?
Summary
The flow of electricity creates a magnetic field. Wherever there is an electric current there is a corresponding magnetic field, and wherever a magnetic field exists, so does an electric field. Every electric field has an equal magnetic field and vice versa. The electric field produced by current flowing through a wire coil must have a corresponding magnetic field. Therefore, a magnetic field is induced. The fields cannot be seen, but the effects of them can be by watching the magnetized needle orient itself in the induced magnetic field. When the wires are connected to the other ends of the battery, the fields are oriented in the opposite direction, so the needle has to respond accordingly. It twists around to point in the other direction.
Source
“Awesome Experiments in Electricity and Magnetism.” Michael DiSpezio, Sterling Publishing Co.: New York, 1998, p. 100. © S. Olesik, WOW Project, Ohio State University, 2001.
Electroscope
Index
An electroscope is an instrument used by scientists to measure the relative strength of an electric charge. A simplified version of an electroscope can be made easily and can be used to study and explore static electric charges.
Materials
Clear plastic cup Aluminum foil Metal paperclip Modeling clay or plastic tape Balloon Scissors
What To Do
Make a small hole in the bottom of the plastic cup through which the paperclip will later be inserted. *Note: Try using a hot glue gun without any glue to melt a small hole, or heat the paperclip and push the end of it through the cup. Cut two strips of foil that measure roughly � inch by 1 � inch. Use the end of a paper clip to punch small holes in the one end of each foil strip. Unfold a paperclip so that it looks like a long J, and hang the foil strips, called leaves, on the curved end of the J. Holding the cup upside-down, insert the straight part of the J paper clip through the hole in the cup, so the leaves hang inside the upside down cup without touching the table or desk top. Secure the paperclip using molding clay or plastic tape. Roll some aluminum foil into a ball and place the ball on the top of the paperclip that is sticking out from the cup. The electroscope is complete and ready for use. Charge a balloon by rubbing it with a piece of wool or fur, or by rubbing it in your hair. Slowly bring the charged balloon near the foil ball on the electroscope and watch how the leaves react. Move the balloon away and observe the leaves of the electroscope.
Questions
1. What made the leaves move? How? Why? 2. Does anything else coming near the foil ball on the electroscope have the same effect? What? 3. Do the leaves move more or less if the balloon is more charged? Why?
Summary
The leaves of the electroscope moved away from each other because they both acquired a negative charge and repelled each other. The negatively charged balloon coming near the foil repelled some of the electrons in the foil. Those electrons travel down the paper clip to the leaves, giving each of them extra electrons and thus a negative charge. Like charges repel, so the leaves moved away from each other.
Source
“Awesome Experiments in Electricity and Magnetism.” Michael DiSpezio, Sterling Publishing Co.: New York, 1998, p. 62-63. © S. Olesik, WOW Project, Ohio State University, 2001.
Lemon Battery
Index
Batteries use chemical reactions to create an electric current. In 1800 Alessandro Volta made the first battery by layering copper and zinc in a jar of salt water. The chemical reaction created the first steady supply of electricity. The steady supply of electricity from batteries is used to power all sorts of electrical devices such as toys, light bulbs, radios, calculators and cars. Following Volta�s example we can make batteries, too.
Materials
6 lemons 7 alligator clips 6 pennies 6 large metal paperclips Knife Voltmeter Light emitting diode (LED) that requires low voltage and low current Calculator that requires low voltage and low current
What To Do
Prepare the lemons for use in the battery by placing the lemons one by one on a flat surface and firmly pushing down on them with one hand while rolling them back and forth. This is to break up the insides of the fruit so the juices can flow more easily. Use a knife to make two small incisions in the middle of each of the lemons. The cuts should be about ďż˝ inch long, deep enough to reach the juicy insides of the fruit, and about ďż˝ inch apart. In each lemon insert a penny into one of the slits so only a small part of the coin remains on the outside of the lemon. Do the same with a paperclip in the other slit. Line up all of the lemons so that the inserts alternate in order (i.e. penny, paperclip, penny, paperclip, penny . . . ).Use an alligator clip to connect the penny from the first lemon to the paperclip of the next lemon. Continue connecting the lemons by using alligator clips to bridge from lemon to lemon, connecting pennies to paperclips. The first and last lemons in the row will have a paperclip and a penny that are not wired to the rest of the battery. Connect an alligator clip to each one to create the leads for the battery. Turn the voltmeter to DC mode and test the lemon battery by connecting the lead wires to the voltmeter. If the voltage is very low test each lemon separately using the wires connected to the penny and paperclip in each lemon. Lemons that are not working well can be adjusted by squeezing them to break up more of the tissue inside, moving the penny and the paperclip, or refastening the wires to the penny and the paperclip in slightly different locations. Also, check that the penny and paperclip do not touch each other directly. Once the lemon battery is working well, as confirmed by the voltmeter, it can be used to power the LED. Gently bend the legs of the LED away from each other. Connect the wire that leads from the paperclip to the side of the LED that is flat and has the shorter leg. Connect the wire from the penny to other leg of the LED. Dim the lights in the classroom and the glow from the LED should be visible.
Questions
1. What else might the lemon battery be able to power? 2. What other types of fruits might be used to make batteries? 3. If more lemons were used to make the battery would the amount of electricity it produced be different? Would the voltmeter show a higher, lower, or the same reading?
Summary
Electricity is the flow of electrons. Electron flow can be produced by some chemical reactions, including this one between zinc from the paperclip, the copper from the penny, and the citric acid in the lemon juice. The chemical reaction takes some positively charged zinc ions from the paperclip, leaving behind an excess of negatively charged electrons. The penny becomes positively charged by drawing positive ions from the lemon juice solution, and then the electrons flow from the negatively charged paperclip to the positively charged penny. This flow of electrons is the electricity produced by the lemon battery.
Extension
What else can the lemon battery power? Remove the battery from a simple calculator and attach wires to the positive and negative terminals for the battery. Connect the lead from the paperclip to the negative terminal and the lead from the penny to the positive terminal of the calculator. Does the calculator work? Try a few calculations.
Source
“How Science Works,” Judith Hann, Reader’s Digest, Dorling Kindersley Limited, 1991, p. 151. “Fruit Cell” in “Awesome Experiments in Electricity and Magnetism.” Michael DiSpezio, Sterling Publishing Company, 1998, p. 102. ISBN 0-8069-9819-9 © S. Olesik, WOW Project, Ohio State University, 2001.
Parallel and Series Circuits
Index
Electricity is used in so many things it must be able to be used in a variety of ways. This experiment shows two different ways electric circuits can be set up, and how they differ.
Materials 2 2 4 4 7
batteries battery holders bulbs bulb holders alligator clips
What To Do
To build the series circuit, connect an alligator clip to a battery and a bulb holder. Then use another alligator clip to connect the bulb to another bulb holder by attaching one end of the clip to one bulb and the other end of the clip to the other bulb. Use a third alligator clip to attach the second bulb to the other side of the battery. With everything connected, both bulbs should light up. But if one of the alligator clips is disconnected, both bulbs go out. The same will happen if one or both of the bulbs are unscrewed. To build the parallel circuit, connect an alligator clip to a battery on one end and to a bulb holder on the other end. Use another alligator clip to attach the other end of the battery to the other side of the same bulb holder. Add a second light bulb to the circuit using two more alligator clips. One of the clips should attach to one end of the first bulb and one end of the second. The other alligator clip should attach to the other sides of both bulbs. With everything connected, both bulbs should light up. If one of the alligator clips is disconnected, will the bulbs still light? What if one of the bulbs is unscrewed? How many wires can be disconnected before the lights go out?
Questions
1. What is the difference between a parallel and a series circuit? 2. Why did a disconnection cause the lights to go out in the series circuit, but not in the parallel circuit? 3. Why are both types of circuits useful in our lives?
Source
“How Science Works,” Judith Hann, Reader�s Digest, Dorling Kindersley Limited, 1991, p. 155. “Edison Etc.” The Wild Goose Company: Salt Lake City, 1994, p. 41-43. © S. Olesik, WOW Project, Ohio State University, 2001.
Simple Circuits
Index
Electricity is used in our homes and schools everyday, but how does it get there? Electricity flows through wires from power plants, into our homes and schools, and through the computers, televisions, stoves and lamps that use it. But is it always flowing? This experiment uses a battery and a light bulb in a simple circuit to show that electricity flows through complete circuits.
Materials 1 1 1 1 2
battery battery holder bulb bulb holder alligator clips
What To Do
Place the battery in the battery holder and the light bulb in the light bulb holder. Use alligator clips to connect one side of the battery holder with one of the metal screws on the light bulb holder, and the other side of the battery holder with the other screw on the light bulb holder. When the connections are made, completing the circuit, the bulb will light. This shows that electricity is flowing through the light bulb. If one of the connections is disrupted the light will go out, indicating that electricity is no longer flowing through the light bulb. Try disconnecting the circuit to see the effect.
Questions
1. Why does the light go out when the bulb is disconnected from the battery? 2. Can you think of anything from home that sometimes has electricity flowing through it, but other times does not?
Source
“The Science Book of Electricity.” Neil Ardley, Harcourt Brace and Company: London, 1991, p. 20-21. © S. Olesik, WOW Project, Ohio State University, 2001.
Static Electricity
Index
Opposites attract. The power of static electricity can be seen by watching oppositely charged objects attract each other or objects with like charges repel. These charges cannot be seen, but their effects can be.A charged balloon can make your hair stick up or push another balloon away. You can use static electricity to make bubbles stay in the air or to guide a Ping-Pong ball around a table without even touching it.
Materials
Balloons String Paper Plastic comb Wool Ping-pong balls Puffed rice Soap bubbles Salt and pepper
What To Do
Blow up a balloon and ask a student to rub it on his or her head. This will give the balloon a negative charge because it picks up electrons from the student’s hair. The hair, now missing some electrons, will be positively charged. The positive charge on the hair and the negative charge on the balloon attract each other, so the hair stands up toward the balloon. Cut paper into very small pieces and make a pile on a desktop or table. Charge a balloon by rubbing it in someone’s hair or by rubbing it with a piece of wool. Hold the charged balloon just above the pile of paper pieces and the paper will jump. First, the paper will be attracted to the negative charge on the balloon so it will jump up and stick to the balloon. But by coming into contact with the balloon the paper picks up some of the negative charge. Since like charges repel, the paper will then jump off of the balloon. Blow up two balloons and tie a separate piece of string around the knot in each of them. Attach one balloon to the underside of a desk or table by taping the string. Make sure the balloon can hang without touching anything else. Rub the hanging balloon with wool to charge it. Charge the second balloon the same way, then hold it by the string. Move the free balloon near the hanging balloon and watch them push away from each other. Their negative charges repel. If a piece of paper is placed between the two balloons they will come together quickly because they will both be attracted to the paper. Remove the paper and they will again repel each other. Charge a plastic comb by rubbing it with wool. Bring the comb near a Ping-Pong ball on a tabletop and slowly move the comb around. Because the ball is attracted to the negative charge on the comb, the ball will follow the comb. Charge a plastic comb by rubbing it with wool. Blow a few soap bubbles into the air and bring the charged comb near one of the bubbles. The bubble will be attracted to the charge on the comb, so with practice the comb can be used to keep the bubble in the air without popping. Catch a soap bubble on the end of the bubble-blowing wand and slowly bring a charged comb or balloon near it. Watch as the bubble distorts and stretches toward the charge until it finally detaches from the wand and pops when it slams into the comb. Separate a mixture of salt and pepper quickly, without touching it by holding a charged comb or balloon over the mixture and slowly bringing it closer. The lighter pepper will be picked up and the heavier salt will be left behind.
Questions
1. Why does your hair stick up when you rub a balloon on it? 2. What else can you make a balloon stick to? How? Why? 3. How can you move a Ping-Pong ball without touching it or the table it is sitting on? How else could this new skill be used? 4. What other tricks can you do using static electricity? 5. Why do the bubbles move and stretch toward the charged balloon or comb? 6. Why is the pepper picked up but not the salt? If there were not any pepper, would the salt be picked up?
Source
“Edison Etc.” The Wild Goose Company: Salt Lake City, 1994, p. 41-43. “The Science Book of Electricity.” Neil Ardley, Harcourt Brace and Company: London, 1991, p. 20-21. © S. Olesik, WOW Project, Ohio State University, 2001.
Index
Supply Lists Circuit Quiz Game Cardstock 2 batteries 2 battery holders 4 alligator clips 1 flashlight bulb 1 bulb holder Aluminum foil Tape Plastic film
Conductors and Insulators 1 battery 1 battery holder 1 flashlight bulb 1 bulb holder 3 alligator clips Cardboard Metal thumbtacks or brads Coins Keys Cork Buttons Fabric Screws Marbles Plastic String
Connect the Circuit Game
Bare wire or metal clothes hanger 1 flashlight bulb 1 bulb holder 2 batteries 2 battery holders Insulated wire Cardboard Tape Clay (if using the clothes hanger) Steel wool (if using the clothes hanger)
Electric Currents and Magnetic Fields 10 yards of insulated copper wire Wire strippers Tape Thread Magnet Beverage can Battery
Electroscope
Clear plastic cup Aluminum foil Metal paperclip Modeling clay or plastic tape Balloon Scissors
Lemon Battery
6 lemons 7 alligator clips 6 pennies 6 large metal paperclips Knife Voltmeter Light emitting diode (LED) that requires low voltage and low current Calculator that requires low voltage and low current
Parallel and Series Circuits 2 2 4 4 7
batteries battery holders bulbs bulb holders alligator clips
Simple Circuit 1 1 1 1 2
battery battery holder bulb bulb holder alligator clips
Static Electricity Balloons String Paper Plastic comb Wool Ping-pong balls Puffed rice Soap bubbles Salt and pepper
References
Index
“Power Up.” Sandra Markle, Atheneum: New York, 1989, p. 24. “The Science Book of Electricity.” Neil Ardley, Harcourt Brace and Company: London, 1991. “Science Experiments with Electricity.” Sally Nankivell-Aston and Dorothy Jackson, Franklin Watts: New York, 2000. “Awesome Experiments in Electricity and Magnetism.” Michael DiSpezio, Sterling Publishing Co.: New York, 1998. “Edison Etc.” The Wild Goose Company: Salt Lake City, 1994. “How Science Works,” Judith Hann, Reader’s Digest, Dorling Kindersley Limited, 1991.
Children’s Literature
Index
“Electricity and Magnetism.” By Peter Adamczyk and Paul-Francis Law. Usborne Publishing Ltd.: London, 1993. “All About Electricity.” By Melvin Berger, illustrated by Marsha Winborn. Scholastic Inc.: New York, 1995. ISBN 0-590-48077-4. “Switch On, Switch Off.” By Melvin Berger, illustrated by Carolyn Croll. Harper & Row, Publishers, Inc.: New York, 1989. ISBN 0-690- 04786-X. “The Magic School Bus and the Electric Field Trip.” By Joanna Cole, illustrated by Bruce Degan. Scholastic, Inc.: New York, 1997. ISBN 0-590-44682-7. “Shocking Science: Fun and Fascinating Electrical Experiments.” By Shar Levine and Leslie Johnstone, illustrated by Emily S. Edliq. Sterling Publishing Co., Inc.: New York, 1999. ISBN 0-8069- 3946-X. “Super-Charged Science Projects: Electromagnets in Action.” By Parramon’s Editorial Team. Barron’s Educational Series, Inc.: Hauppauge, 1994. ISBN 0-8120-6437-2. “Electricity.” By Simon de Pinna, photography by Chris Fairclough. Raintree Steck-Vaughn Publishers: Austin, 1998. ISBN 0-8172- 4945-1. “The Usborne Illustrated Encyclopedia: Science and Technology.” Usborne Publishing: London, 1996. “The Usborne Internet-Linked Library of Science: Light, Sound & Electricity.” By Kirsteen Rogers, Phillip Clarke, Alastair Smith, and Corinne Henderson. Usborne Publishing: London, 2001. “Fascinating Science Projects: Electricity and Magnetism.” By Bobbi Searle. Copper Beech Books: Brookfield, 2002. ISBN 0-7613- 1630-2. “Electricity and Magnetism.” By Robert Snedden. Heinemann Library: Chicago, 1999. ISBN 1-57572-868-0. “Janice Van Cleave’s Electricity: Mind-Boggling Experiments You Can Turn Into Science Fair Projects.” By Janice Van Cleave. John Wiley & Sons, Inc.: New York, 1994. ISBN 0-471-31030-7.
Index
Notes
There are currently no notes on this unit. If you have suggestions or changes to make on the experiments or units, please email us! Our address is wow@chemistry.ohio-state.edu. S. Olesik, WOW Project, Ohio State University, 2002.
Copyright Š 2002-2010 by S.Olesik, Wonders of Our World Project (WOW), the Ohio State University. Permission to make digital or hard copies of portions of this work for personal or classroom use is granted without fee provided that the copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page in print or the first screen in digital media. Abstracting with credit is permitted.
18