1. SHPE Foundation Online SHPE Jr. Member Activities TeachEngineering Hands-on Activity: * Yogurt Cup Speakers TeachEngineering Digital Library: teachengineering.org teachengineering.org

2. TeachEngineering Digital Library The TeachEngineering digital library provides ~ 1,400 free engineering lessons and activities. Engineering lessons and activities connect real- world experiences with curricular content already taught in K-12 classrooms. TeachEngineering's comprehensive curricula are hands-on, inexpensive, and relevant to students' daily lives. SHPE Foundation Online SHPE Jr. Member Activities http://www.teachengineering.org

3. Yogurt Cup Speakers Learn about electricity and magnetism by building speakers! Engineering focus: o Engineering Analysis: Build and test speakers while learning about properties of magnets and electromagnets. Learning objectives: o Create an electromagnetic field by running current through a wire coil. o Explain that electric currents produce magnetic fields. The stronger the current, the more intense the magnetic field. o Explain how electricity and magnetism are related concepts. o Describe properties and characteristics of magnets: Magnets can be permanent or temporary Magnets and electromagnets attract or repel each other; similar poles repel, while dissimilar poles attract. Magnets and electromagnets attract or repel another objects. Magnets and electromagnets exert forces at a distance through magnetic fields. SHPE Foundation Online SHPE Jr. Member Activities Reference Activity on TeachEngineering

4. Suggested time: 60 minutes SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Materials o 2 round magnets (½ to ¾ inch diameter) o 10 feet of coated 20-gauge wire o sandpaper o paperclips o 1 plastic container (yogurt, etc.) or plastic cup o 1 D-cell battery o electrical tape o radio with detachable speakers

5. SHPE Foundation Online SHPE Jr. Member Activities Engineering Connection (Real World Application): The study of electromagnetism is the foundation of electrical engineering. In addition, it finds wide application in other engineering disciplines. For example, electromagnets are essential to the design of electric generators and electric motors and therefore to the work of mechanical engineers. They are also used by aerospace engineers as electromagnetic propulsion systems can provide moving power for spacecraft. Yogurt Cup Speakers Electric motor Spacecraft launch

6. SHPE Foundation Online SHPE Jr. Member Activities Vocabulary Terms Definitions magnet An object that is surrounded by a magnetic field and has the property of attracting iron, steel, or other magnets. electromagnet A magnet consisting of a coil of insulated wire wrapped around a soft iron core that is magnetized only when current flows through the wire. magnetic field A region in which magnetic forces can be observed. magnetic force The force exerted between magnetic poles or between two electrically charged moving particles (protons and electrons). current A flow of electrical charge carriers. The common symbol for current is the uppercase letter I. The standard unit is the ampere symbolized by A. Yogurt Cup Speakers

7. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: For this activity, it’s important to understand electromagnets and permanent magnets and the difference between the two. A permanent magnet always has a magnetic field and always displays magnetic behaviors (hence the name “permanent”!).

8. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers An electromagnet is created with a battery (or some other source of electricity) and a wire. A battery has two ends, positive and negative. Although electrons collect at the negative end of the battery, they can flow to the positive end through a wire. The flowing electrons generate a magnetic field. The magnetic field from one wire is quite small. By putting many wires next to each other, a much larger field is created. This is done by making the wire into a coil with many loops. The amount of current that flows through the wire affects the strength of the electromagnet, and the electromagnet only acts as a magnet and produces a magnetic field when current is flowing through the wire.

9. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field.

10. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field. The field from the electromagnet is attracted or repelled from the field of a permanent magnet in the center of the speaker.

11. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field. The field from the electromagnet is attracted or repelled from the field of a permanent magnet in the center of the speaker. When the current in the coil changes, so does the strength of the magnetic field.

12. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field. The field from the electromagnet is attracted or repelled from the field of a permanent magnet in the center of the speaker. When the current in the coil changes, so does the strength of the magnetic field. When the strength of the magnetic field changes, the attractive force between the coil and the permanent magnet changes.

13. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field. The field from the electromagnet is attracted or repelled from the field of a permanent magnet in the center of the speaker. When the current in the coil changes, so does the strength of the magnetic field. When the strength of the magnetic field changes, the attractive force between the coil and the permanent magnet changes. The changing force makes the speaker vibrate and produce sound. The bigger the vibrations, the louder the sound.

14. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Introduction: The idea behind an electromagnet in a speaker is simple: By running electric current through a wire coil, you can create a magnetic field. The field from the electromagnet is attracted or repelled from the field of a permanent magnet in the center of the speaker. When the current in the coil changes, so does the strength of the magnetic field. When the strength of the magnetic field changes, the attractive force between the coil and the permanent magnet changes. The changing force makes the speaker vibrate and produce sound. The bigger the vibrations, the louder the sound. Electromagnets are also used inside televisions to generate pictures, in electric motors, and in some medical devices.

15. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Speakers:

16. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers What are the advantages of using an electromagnetic compared with a regular (permanent) magnet? With a regular magnet, the magnetic field is permanent or "always on". However, with an electromagnet, only when electrical current is flowing through the wire coil is there a magnetic field. This property makes electromagnets more useful than permanent magnets in many applications. For example, a big electromagnet on the end of a crane can lift and drop large masses of iron such as junk cars in a scrap yard.

17. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers Three factors that increase the strength of an electromagnet are: 1) increasing the current flowing through the coil, 2) increasing the number of coils, and 3) putting an iron core inside the coil.

18. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers How can the direction of the magnetic field of an electromagnet be determined? The magnetic field's direction and magnitude depend on the magnitude of the current and the direction of the current. The direction of the magnetic field can be determined by using the right hand rule : Place the wire in your hand with your thumb in the direction of the current [point your thumb from positive (+) to negative (-)]. Close your hand so that your fingers wrap around the wire. Your fingers are pointing in the direction of the magnetic field lines.

19. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers How do speakers work? Electromagnets can be used to make speakers! A sound is produced when a vibrating object moves the air particles around it, which in turn move the air particles around them. Our ears pick up these fluctuations in air pressure and translate them into signals the brain can process.

20. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers A speaker takes the electrical signal and translates it back into physical vibrations to create sound waves. Traditional speakers do this with a driver. The driver includes a permanent magnet and an electromagnet called a voice coil. The driver produces sound waves by rapidly vibrating a flexible cone that is connected to the voice coil. The voice coil is a basic electromagnet. This electromagnet is under the influence of a constant magnetic field created by a permanent magnet. These two magnets interact with each other in the usual way: The positive end of the electromagnet is attracted to the negative pole of the permanent magnet and repelled by its positive pole.

21. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers How do speakers work? A stereo signal constantly reverses the flow of electricity, switching the north and south ends of the electromagnet. In this way, the alternating current constantly reverses the magnetic forces between the voice coil and the permanent magnet rapidly pushing the coil back and forth. When the coil moves, it pushes and pulls on the speaker cone. This vibrates the air around the speaker and creates sound waves, which is what you hear! The bigger the vibrations, the louder the sound. Electromagnets are also used inside televisions to generate pictures, in electric motors, and in some medical devices

22. SHPE Foundation Online SHPE Jr. Member Activities Procedure Overview o Build an electromagnet, study its interactions with a permanent magnet, and then use this knowledge to build a working speaker. Yogurt Cup Speakers Procedure 1.Start by exploring the effects the magnets have on each other when similar poles are near each other (such as either north to north or south to south). Notice the effects the magnets have on each other when dissimilar poles are near each other (such as either north to south or south to north). 2.Create electromagnets by winding roughly 6 to 15 feet of wire around a cylindrical object such as a C- or D-cell battery (see photo). Leave two inches of wire hanging off at each end.

23. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers 3.While keeping the wire in the shape of a coil, carefully remove the wire from the cylindrical object and tape the coil so it does not unravel. 4.Rub a piece of sandpaper on each free wire end to remove the enamel insulation. Remove about 1 inch of insulation from each end. 5.Hold the ends of the wire to opposite ends of the battery to make a series circuit with the battery and the coil. Move the coil close to the magnet and observe its motion. Hook the battery up differently and see what happens to the magnets. (When the coil is connected to the battery in one way, one side of the coil is the north pole and the other side is the south pole of the electromagnet. The north pole of the electromagnet will be attracted to the south pole of the permanent magnet. When the battery is turned around, the poles of the electromagnet are reversed.)

24. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers 6.Attach the coil and a permanent magnet to the bottom of the container with either tape or hot glue. Attach the coil and magnet in such a way that the coil and magnet are next to each other. There are many different creative ways to do this that will work. Examples are shown below.

25. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers 7.Connect the ends of the speaker wire to the speaker output of the radio. On the back of the radio, look for plugs to connect the speaker wires to. These are usually holes that the wires are pushed into. Choose the plugs for one speaker (the left, for example) and insert one end of the wire from the yogurt speaker into one hole, and the other end of the wire into the other (see photo below).

26. SHPE Foundation Online SHPE Jr. Member Activities Yogurt Cup Speakers 8.Turn the radio on and adjust the volume. When more current flows through the wire coil, the electromagnetic force increases. As the radio changes the current very fast, the changing electromagnetic force causes the plastic cap to vibrate. The vibration creates sound waves in the air, which are heard. 9.The wires of the speaker may get hot. When electric current flows through the wire, some of the electrical energy is converted to heat energy due to the résistance inside the wire. If you touch the wire, the heat will transfer to your skin. When the volume of the radio is turned up, more electricity flows through the wire and more heat is generated. If the speaker gets too hot, turn down the volume.

27. SHPE Foundation Online SHPE Jr. Member Activities Safety Issues The home-made speaker wires may get hot when they are attached to the radio. This is more likely to occur with very thin wires and very high-power radios that are set at a high volume. Yogurt Cup Speakers Troubleshooting Tips Make sure to completely remove insulation from the wire ends or no current will flow.

28. SHPE Foundation Online SHPE Jr. Member Activities Now try this!: Try the following extra investigations once you have completed your speakers. Change the amount of current by using more than one battery and monitor the changes in the speaker's movement. Change the direction of the current by changing the wire connections to the battery and monitor the change in the speaker's movement. Can you relate the current's change in direction or change in amplitude to the change in movement in the speaker? Yogurt Cup Speakers

29. SHPE Foundation Online SHPE Jr. Member Activities Now try this!: Try the following extra investigations once you have completed your speakers. When the speaker is connected to the radio, change the volume or add more than one magnet. Can you explain why the speaker gets louder or softer? Yogurt Cup Speakers

30. SHPE Foundation Online SHPE Jr. Member Activities Now try this!: Try the following extra investigations once you have completed your speakers. When the speaker is connected to the radio, change the volume or add more than one magnet. Can you explain why the speaker gets louder or softer? (Answer: When the radio volume is turned up, more electrical current flows through the wire. More current makes the electromagnet stronger. The stronger the electromagnet, the more it is attracted to the regular magnet on the speaker. This makes the vibrations of the speaker bigger and the speaker volume louder. Using more than one permanent magnet or a stronger one also increases the attraction to the electromagnet so that also increases the sound from the speaker.) Yogurt Cup Speakers

31. SHPE Foundation Online SHPE Jr. Member Activities Activity Extensions Make another coil with more windings to wrap around the cell battery. Dissect a real speaker and compare to the one created in this activity. Observe the interaction between two electromagnets. Connect multiple round magnets to the yogurt cup. (Expect the speaker to be louder.) For more challenge, knowing that three variables influence these electromagnetic coils/speakers (current, number of coils and direction of current ), devise your own experiments to test each of the variable influences. Yogurt Cup Speakers

32. TeachEngineering Contact Information TeachEngineering: http://www.teachengineering.org/http://www.teachengineering.org/ o ~1,400 standards-based engineering lessons and activities Carleigh Samson, TeachEngineering Editor o carleigh.samson@colorado.edu carleigh.samson@colorado.edu o 303.492.6950 SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Questions?