Yogurt Cup Speakers. Your Activity Understand the role of electricity and magnetism by building a basic speaker. Material. Create.

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1 Yogurt Cup Speakers Your Activity Understand the role of electricity and magnetism by building a basic speaker Material 2 round magnets (1/2 to ¾ inch) 15 ft, gauge coil wire 1 plastic container 1 D-Cell battery Sandpaper Electric Tape Create 1. Wind roughly 6 to 15 feet of wire around a cylindrical object such as C or D cell battery. Leave 2 inches of wire hanging off at each end 2. 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. 3. Rub a piece of sandpaper on each free wire end to remove the enamel insulation. Remove about 1 inch of insulation from each end. 4. Hold the ends of the wire to opposite ends of the battery to make a series circuit with the battery and the coil 5. 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. 6. 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. 7. Turn the radio on and adjust the volume. Do you hear anything? Science Topics Electrical Engineering, Electromagnetism What s going on? You have basically built an electric motor that 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. 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. There are three variables that influence electromagnetic coils/speakers (current, number of coils and direction of current).

2 Yogurt Cup Speakers Activity Lead Notes Introduction This is an extension to the Electric Motor activity. Students investigate motors and electromagnets as they construct their own simple electric motors using batteries, magnets, paper clips and wire. Can you imagine life without radios? Do you know that the object that makes the speaker in the radio work is an electromagnet? 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. The easiest way to do this is by making the wire into a coil with many loops. 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. Now that you know some applications of electromagnets, can you say what the difference between a regular magnet and an electromagnet is? A magnet is any material that has a magnetic field. 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. 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. Learning Objectives After this activity, students should be able to: Understand the role electricity and magnetism plays in speakers Explore the properties of magnets, create electromagnets and determine the direction of magnetic fields Monitor changes in the speaker s movement as the amount or the direction of the current change Materials Each student/group of students need: 2 round magnets (1/2 to ¾ inch) 1 plastic container (yogurt cup) 15 ft gauge coil wire 1 D cell battery For the entire class to share:

3 Fine sandpaper Electric Tape Wire cutters Scissors A few compasses (optional) Preparing Materials Set out pairs of magnets at each table. Briefly review magnets and their polarities. (optional) Bring out a speaker radio and have it playing some music. Notes about Materials Ask students to be very careful when using the sharp wire strippers and wire cutters. Ask students to not play with the insulated wire; they might poke or cut themselves or another student. Vocabulary Battery: Commutator: Current: Engineer: Insulated wire: Magnet: Magnetic field: Motor: North pole: Solenoid: South pole: Uninsulated wire: A cell that provides electric current. A cylindrical arrangement of metal bars connected to the coils of a DC (direct current) motor that provides for a reversal of current into the coils of the motor with every half spin, allowing the motor to spin continuously in one direction. A flow of electrons. A person who applies scientific and mathematical principles to creative and practical purposes such as the design, manufacture and operation of efficient and economical structures, machines, processes and systems. Wire that is covered with a coating of some kind. Something that attracts iron and generates a magnetic field. The field generated by a magnet or by an electric current. An electrical device that converts electrical energy into mechanical energy. The end of a magnet that points north. A coil of insulated wire. The end of a magnet that points south. Wire that is not covered with a coating

4 Background How can the direction of the magnetic field of an electromagnet be determined? Similar poles on magnets repel, while dissimilar poles attract. Running current through a wire creates a magnetic field similar to a field of a magnet. That 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. How do speakers work? 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. 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. 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. Activity Sheet None Conduct Experiment Kids use the procedure in the handout to create the motor. More detailed instructions available here.

5 Discuss student observations 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? 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. 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. (The speaker should be louder.) Activity Scaling For lower grades and younger students, this activity may be too challenging. Two alternate options include: make the wire coils in advance and have students put together the yogurt cup speakers as a group; or complete the activity as a class demonstration. Source