Grade Level: 9th - 12th; Type: Physics, Physical Science
To determine how a microphone works...
Questions for Background Research:
- What is a microphone?
- Who invented the microphone?
- What are transducers?
- How do sound waves differ from electrical currents?
- What are some practical applications of microphones? In what other devices and instruments are they found?
- What is meant by amplification?
- Of what practical value are amplifying devices?
- What are some of the basic components of hearing aids?
On the information level, this experiment serves to acquaint the student with basic information on how a microphone amplifies the sounds it receives. A microphone is a transducer. A transducer is a device that converts sound energy into electrical energy. Microphones are used in many other instruments and devices such as tape recorders, telephones, hearing aids and tape recorders . For example, in the telephone, your speech is converted into electrical impulses which are then converted at the other end by another transducer in the receiver`s earpiece.
This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control when required, of identifying dependent and independent variables, of selecting a large enough sample of subjects when applicable to the objective, of accurate and organized data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as scientist.
24" of 30AWG enamel magnet wire (from Radio Shack, p/n 278-1345B), 1.5" brass-coated steel brad, 1 ceramic magnet, 0.5" diameter, 3/16" thick (from Radio Shack, p/n 64-1883), a 1.5" square piece of 100 grit sandpaper and a Styrofoam cup .
- Gather all (#28-#32) (from Radio Shack, p/n 278-1345B 1 ceramic magnet, 0.5" diameter, 3/ 16" thick (from Radio Shack, p/n 64-1883), a 1.5" square piece of 100 grit sandpaper, 2, a tape recorder or a radio and an old speaker .You may wish to take photos of the materials you used and the steps you took in building your own working speaker so that others who wish to replicate the project may readily do so.
- Start by cutting a 15 cm length of the 3/16inch dowel rod. Now, cut a 1.9 cm length of the 3/ 4inch dowel rod. Drill a hole in one end of the large dowel rod and insert the small dowel in the hole. Glue it in place.
- Now cut two cardboard disks each one 2.5 cm in diameter. Cut a hole in the middle of one disk so that the 3/16 inch dowel can go through. On the same disk, make a small notch on the outside .This is for the wires to pass through .Glue the disks to each end of the ¾ inch dowel. The disks will help you to keep the wire in place so that you can wind it into a coil.
- Take the roll of enameled copper wire (#28-#32). Leave a 10 cm free lead, wind a 100 turn coil on the thicker dowel. Leave another 10cm lead at the end of the coil. Bring the leads through the Notch. Tape both to the 3/16 inch dowel stick. Do not put tape at the ends of the wire.
- Using the fine sandpaper, r emovethe enamel from the last 1cm of each lead. Make a cord using a 3mm standard earphone plug and two conductor wires. Solder each wire to the ends of the coil. Plug the earphone plug into either a radio or you may use a tape recorder.
- Put a piece of straw over the end of the smaller diameter dowel.
- Turn on the radio or the tape recorder and bring a magnet close to the coil while holding the dowel in your teeth. Listen! What did you hear? Move the magnet away. What did you hear? Explain what happened.
- Have some stand next to you. Ask him or her they heard. Explain what happened.
- You will observe that the coil is vibrating, moving back and forth. This is due to the fact that an electric current is flowing back and forth. This is how a speaker works. A piece of cardboard when glued to the speaker coil moves the air back and forth and the result is that you hear sound.
- Examine an old speaker. See if you can locate the coil and the magnet. Illustrate what you have observed.
- Write up the experiment. Post the photos you have taken.
- Demonstrate what you have done o your class. Ask for their questions and responses.
Data: Observations & Responses
|Brought magnet close? What happened?|
|Observer close to you! What did he /she hear?|
Terms/Concepts: Microphone, sound waves, electricity, electric currents, transducers
Experiment excerpted and adapted from Eisenkraft, Authur, Active Physics, Tooth Tunes: The inner Ear and Transducers, pp. 53-54.