Piezoelectricity: how do we measure it?

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Discussion Overview

The discussion revolves around measuring the voltage generated by piezoelectric crystals when subjected to mechanical stress. Participants explore methods for effectively capturing and displaying this voltage in a classroom demonstration setting, focusing on the challenges faced in obtaining stable readings during the experiment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant describes an experiment using a piezoelectric crystal from a gas lighter and notes that the voltage reading decreases rapidly when the load is applied, leading to difficulties in measurement.
  • Another participant suggests that the voltmeter should maintain the voltage due to its high resistance, questioning whether the voltage drop is due to charge flowing through the voltmeter.
  • Several participants propose using an oscilloscope as a solution to capture voltage changes more effectively, indicating that it can show voltage fluctuations clearly when measuring piezoelectric devices.
  • There is mention of needing a source of vibration to enhance the demonstration, with one participant sharing their experience of using hand squeezing to generate measurable voltage changes.

Areas of Agreement / Disagreement

Participants express varying opinions on the best method to measure the voltage from piezoelectric crystals, with no consensus on a single solution. The discussion includes both the use of voltmeters and oscilloscopes, indicating differing preferences and experiences.

Contextual Notes

Participants do not fully resolve the issue of voltage measurement stability, and there are assumptions about the behavior of voltmeters and oscilloscopes that remain unexamined.

Who May Find This Useful

This discussion may be useful for educators and students interested in experimental physics, particularly those looking to demonstrate piezoelectricity in a classroom setting.

markuz
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Hello everyone, I am running a physics class next week where I want to show to high school children the power of piezoelectricity.
I want to let them see with their own eyes that if a crystal is squeezed the differential potential between two opposite faces will change accordingly to the amount of deformation (load) the crystal undergoes. So I took off a bit of crystal from a gas lighter, connected to electrodes to opposite faces to measure the voltage with a multimeter.
What I found out doing the experiment is that the crystal do get charged as soon as the load is applied, but the voltage is rapidly decreasing (obviously because all the charge travel across the circuit to produce the reading); sometime it is so fast that I cannot get the reading at all. Anybody knows a better way to get such voltage gauge in such short amount of time (b.t.w. I am using both an analogue voltmeter and a multimeter to get the readings)?
Any suggestion appreciated.
Thanks
 
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Not familiar with the level of voltage you get from one, but surely the voltmeter should present such a high resistance that the voltage is maintained? Are you saying the voltage is dropping because the charge is flowing through the voltmeter?
 
Right what I need is a (maybe cheap) oscilloscope
 
markuz said:
Right what I need is a (maybe cheap) oscilloscope
An oscilloscope will show a voltage change very easily. In ~cm sized, cylcindrical piezo devices I've used in the past, a 'scope on the 100 mV/div setting showed a several divisions deviation from squeezing the device by hand. Nice easy way to test that you have made good solder connections to the piezo.
russ_watters said:
...and a source of vibration
Squeezing by hand was always enough for me.
 

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