$3-5/speaker 60 min Magnet Wire - Sandpaper

Transcription

1 DIY Speakers Topic Area(s) Cost Time Grade Level Supplies Electromagnetism Sound Electrical Circuits Prototyping & Making $3-5/speaker 60 min Magnet Wire - Sandpaper - D-cell battery (or similar sized cylinder) - Headphone/speaker plug - Alligator clips - Electrical tape - Neodymium magnet - Paper or foam cup/plate - Working audio device with a headphone plug Curriculum Links Science o Grade 6 and 7 Curricular Competencies: Planning and conducting, applying and innovating o Grade 7 Big Ideas: The electromagnetic force produces both electricity and magnetism. o Grade 7 Content: Electricity - electromagnetism Applied Design, Skills and Technologies o Grade 6 and 7 Curricular Competencies: Prototyping, testing, making o Grade 6 and 7 Content: Power technology - forms of energy, devices that transform energy Materials (for each student or group) Magnet wire - 24-gauge or higher (thinner) m Sandpaper (5-8 cm square) D-cell battery or similar sized cylinder 3.5mm male audio cable (may also be called headphone, speaker or auxiliary cable) Two alligator-clip leads Electrical tape (or scotch or masking tape) 1 or 2 neodymium magnets Paper cup (or plate) Working audio device with headphone plug (such as a phone or radio) - can be shared among all groups 1

2 Background Information Magnetism Magnets are objects or devices that give off an external magnetic field. These fields attract ferrous objects like pieces of iron, steel, and nickel. Every magnet has two poles: North-seeking and South-seeking. Opposite poles attract, while similar poles repel. The needle of a compass is an example of a magnet. Electromagnetism is an example of a fundamental force. The other fundamental forces are gravity, strong nuclear force and weak nuclear force. Magnetic fields are lines of force that move from the North Pole of a magnet to the South Pole. The lines of force never cross each other. If you put a compass along a magnetic field, it will align itself tangent to the line of force at that point. These fields are not related to gravity. The strength of magnetic force on an object depends on the distance between the object and the magnet. Many magnets are permanent, meaning they never lose their magnetism. Objects and materials can also be temporary magnets ; they can act like permanent magnets while in a strong magnetic field, but will lose this ability once out of range of that field. Examples of temporary magnets include paper clips, and iron nails. 2

3 Electromagnetism Another way to generate magnetic fields is by moving charges (electrons). This is also known as using electricity. Whenever an electric current runs through a wire, a magnetic field is generated around it as electrons move from the source through the circuit. Figure 2: Electromagnetic fields between a positive charge and a negative charge A simple electromagnet can be created by wrapping an iron nail with insulated copper wire, removing insulation at the wire's end, and attaching the wire ends to a battery with tape. The nail is now a temporary magnet, as the electricity flowing through the wire creates a magnetic field. When the wire is disconnected from the battery, the nail loses its magnetic properties. An electromagnet's strength can be changed by altering the amount of current flowing through it, or by the number of times the wire is coiled. Each time a coil is wrapped around, it increases the strength of the electromagnet's magnetic field. Figure 3: An electromagnet using a nail by Gina Clifford (CC BY-NC-ND 2.0) via Flickr 3

4 The poles of an electromagnet are not static; they can be reversed by changing the direction of the flow of electricity. Electricity can be generated by changing a pattern of magnetism. This is the general principle behind generators, which generate alternating current (AC) power. Procedure 1. Sand the enamel off the last 5 cm of each end of the magnet wire until the bare wire gleams at both ends. 2. Wind the magnet wire around the battery, leaving 4 in (10 cm) free at each end. 3. Slide the wire off the battery and wrap the free ends around the coil to keep the arrangement in place. Leave a few inches of wire sticking out either end of the coil. 4. Tape the coil to the outside bottom of the paper cup. 5. Attach an alligator clip to each of the two protruding ends of the wire coil. 6. With scissors or wire strippers, strip off the ends of the audio cable wire and separate the two strands. 7. Attach the free end of the alligator clip leads to the two strands of wire on the audio plug. 8. Plug the audio plug into your phone (or another device) and turn on some music. You may have to turn up the volume louder than you normally would. 9. With one hand, hold the cup close to your ear. With the other hand, bring the magnet closer to the coil under you can hear sound from your speaker. Source: 4

5 Extensions: - Try using different cup materials (plastic, foam, paper). Which material(s) make the best speakers? - Try making the coil with more or less wire. Which speakers are louder? Which are quieter? - Try using your speaker as a microphone. Does it work? What Happened? Speakers transform electricity into sound. The speaker contains an electromagnet (the coil) and a permanent magnet. When electrical current flows through the coil, a magnetic field is generated. This magnetic field attracts and repels the permanent magnet, causing it to vibrate back and forth. The cup (or plate) the coil is attached to amplifies these vibrations which pushes the air back and forth and creates sound waves that travel to your ears. The frequency of the vibrations (how many times it vibrates each second) changes the pitch of the sound and their amplitude (how far the coil travels back and forth) changes the volume. Microphones use the same parts, but in reverse! Speaking into a microphone causes it to vibrate, which moves the coil through the permanent magnet s magnetic field. This in turn causes current to be generated in the coil. The current generated in the coil is recorded by the phone or recorder as a sound file. Connecting Engineering to Your Classroom This is one example of a practical use of electromagnetism. Other uses include electric motors (like those found in washing machines, blenders or the vibrate function of your phone). Electromagnetism is also used in generators. Generators produce and supply our communities with the electricity we need.bc Hydro offers free resources to teacher about hydroelectricity. Visit for more information. 5