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Microphones
5 questions By Tony R. Kuphaldt
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Question 1 of 5
Explain how a moving-coil, or dynamic microphone works. Identify how the principle of electromagnetic induction is put to practical use in this device.
Reveal answerA moving-coil microphone is built just the way the name suggests: a lightweight coil of wire gets moved past a magnet in proportion to vibrations in the air (sound), generating an AC voltage representative of the sound wave oscillations.
Follow-up question: characterize the typical output impedance of this microphone type. Is it generally considered a low-impedance or a high-impedance type of microphone? Why do you think this is?
Notes:Ask your students where they located this information. it is important for students to learn where and how to research for needed information.
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Question 2 of 5
Certain substances are known to physically deform (shorten or lengthen) when an electrical voltage is applied across their length. The effect is known as piezoelectricity. What types of substances are known to be piezoelectric? Identify some possible applications of this phenomenon.
Reveal answerCertain crystal substances, such as quartz, are known to be piezoelectric.
Notes:As your students will no doubt discover in their research, piezoelectricity is a two-way effect: physical motion from electricity and visa-versa. It will be clear how well they did their research by the types of applications they think of for the “electricity-to-motion” form of piezoelectricity, given the typical physical scale of piezoelectric displacements.
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Question 3 of 5
Explain how a crystal microphone works. Identify how the principle of piezoelectricity is put to practical use in this device.
Follow-up question: characterize the typical output impedance of this microphone type. Is it generally considered a low-impedance or a high-impedance type of microphone? Why do you think this is?
Reveal answerIn a crystal microphone, a small piezoelectric crystal is stressed and unstressed by sound wave pressure, generating a voltage representative of the sound wave oscillations.
Notes:Ask your students where they located this information. it is important for students to learn where and how to research for needed information.
