1. Now, I know that a piezoelectric material converts mechanical force resulting in a deformation into electrical potential, but does it do this WHEN the force is applied, or AS LONG AS the force is applied.

Example: if you placed a brick on a small piezoelectric generator, would it produce a momentary charge when you placed the brick on it and then nothing, or would it start producing a constant charge as long as the brick was sitting on top of it?

Thanks.

2.

3. Originally Posted by pippinj
Now, I know that a piezoelectric material converts mechanical force resulting in a deformation into electrical potential, but does it do this WHEN the force is applied, or AS LONG AS the force is applied.

Example: if you placed a brick on a small piezoelectric generator, would it produce a momentary charge when you placed the brick on it and then nothing, or would it start producing a constant charge as long as the brick was sitting on top of it?

Thanks.
You might just consider doing a little bit of research on your own. Here is a start.

http://en.wikipedia.org/wiki/Piezoelectricity

4. I did that first, but it wasn't entirely clear to me, so I came and asked here for clarification.

5. Originally Posted by pippinj
I did that first, but it wasn't entirely clear to me, so I came and asked here for clarification.

6. Originally Posted by pippinj
Now, I know that a piezoelectric material converts mechanical force resulting in a deformation into electrical potential, but does it do this WHEN the force is applied, or AS LONG AS the force is applied.
I read the article again, question's still the same.

7. Originally Posted by pippinj
Originally Posted by pippinj
Now, I know that a piezoelectric material converts mechanical force resulting in a deformation into electrical potential, but does it do this WHEN the force is applied, or AS LONG AS the force is applied.
I read the article again, question's still the same.
There is no way that you read that article and thought about it in any depth in the time between when I made my post and you repeated your question. In fact, had you done that you would either have answered your own question or been able to ask a more specific and informed question.

In short, you are not telling the truth and are intellectually lazy. You need to do some thinking on your own and not expect to have knowledge handed to you on a platter.

8. Holy crap, relax. I didn't have to read the entire thing, as I had already read it before asking here. But fine, you want specifics, here you go:

"Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins)[1] in response to applied mechanical strain.
...
Of decisive importance for the piezoelectric effect is the change of polarization P when applying a mechanical stress. This might either be caused by a re-configuration of the dipole-inducing surrounding or by re-orientation of molecular dipole moments under the influence of the external stress. Piezoelectricity may then manifest in a variation of the polarization strength, its direction or both, with the details depending on 1. the orientation of P within the crystal, 2. crystal symmetry and 3. the applied mechanical stress. The change in P appears as a variation of surface charge density upon the crystal faces, i.e. as a variation of the electrical field extending between the faces, since the units of surface charge density and polarization are the same, C/m2] = [Cm/m3]. However, piezoelectricity is not caused by a change in charge density on the surface, but by dipole density in the bulk. For example, a 1 cm3 cube of quartz with 2 kN (500 lbf) of correctly applied force can produce a voltage of 12500 V.[6]"

Still doesn't say whether the charge produced is constant or momentary.

Take a look, and you might find that the spade work has been done already, but apparently you're too busy doing... whatever... to actually comprehend what other people have written.

Seriously, though, if you don't want to answer my question, don't bother. It's no skin off your nose not to. Certainly better than attacking people for asking an honest question.

9. Originally Posted by pippinj

Still doesn't say whether the charge produced is constant or momentary.
Yes it does.

Read the article with some thought.

Also think a bit about the (false) statement that the applied stress results in charge accumulation. There are no more electrons present after the stress is applied than before -- think about the statement regarding polarization and what that means.

BTW reading is not a passive exercise. You have to engage your brain and try to reason through what you read. Cutting and pasting quotes is not a sign of comprehension.

10. Originally Posted by DrRocket
Originally Posted by pippinj

Still doesn't say whether the charge produced is constant or momentary.
Also think a bit about the (false) statement that the applied stress results in charge accumulation. There are no more electrons present after the stress is applied than before -- think about the statement regarding polarization and what that means.
No, there aren't any more electrons, but the electrons there are induced to move from one part of the material to another. Thus there is electrical potential. When a conductor is attached at both points, the electrons are provided with an easy path between them, and so we have a usable electric current. What I don't understand, what I'm asking clarification on, is: will this tendency of electrons to move continue to be manifest, or will it die down with the material effectively coming to a new "resting state".
[/quote]
BTW reading is not a passive exercise. You have to engage your brain and try to reason through what you read. Cutting and pasting quotes is not a sign of comprehension.[/quote]
If I had completely comprehended the section quoted, I wouldn't be here asking for clarification, would I.

11. Originally Posted by pippinj
Originally Posted by DrRocket
Originally Posted by pippinj

Still doesn't say whether the charge produced is constant or momentary.
Also think a bit about the (false) statement that the applied stress results in charge accumulation. There are no more electrons present after the stress is applied than before -- think about the statement regarding polarization and what that means.
No, there aren't any more electrons, but the electrons there are induced to move from one part of the material to another. Thus there is electrical potential. When a conductor is attached at both points, the electrons are provided with an easy path between them, and so we have a usable electric current. What I don't understand, what I'm asking clarification on, is: will this tendency of electrons to move continue to be manifest, or will it die down with the material effectively coming to a new "resting state".
BTW reading is not a passive exercise. You have to engage your brain and try to reason through what you read. Cutting and pasting quotes is not a sign of comprehension.[/quote]
If I had completely comprehended the section quoted, I wouldn't be here asking for clarification, would I.[/quote]

If you had comprehended anything you would realize that the piezoelectric effect inducs a charge imbalance in the material and does not directly create a current. That charge imbalance will remain so long as the stress is maintained. Creation of a current requires a source of mobile electrons to be affected by the resulting magnetic field -- rather like charging a capacitor. That source of electrons is typically due to a connection of a conducting metal to the piezoelectric crystal so that you get a transient current but not a steady-state current.

In short the answer to your question is "none of the above" and you need to look more deepy at the phenomenon involved. There is no net charge produced, only a charge imbalance --- hence the issues involving polarization in the article that you have failed to spend the time to understand.

12. Originally Posted by DrRocket

If you had comprehended anything you would realize that the piezoelectric effect inducs a charge imbalance in the material and does not directly create a current. That charge imbalance will remain so long as the stress is maintained. Creation of a current requires a source of mobile electrons to be affected by the resulting magnetic field -- rather like charging a capacitor. That source of electrons is typically due to a connection of a conducting metal to the piezoelectric crystal so that you get a transient current but not a steady-state current.

In short the answer to your question is "none of the above" and you need to look more deepy at the phenomenon involved. There is no net charge produced, only a charge imbalance --- hence the issues involving polarization in the article that you have failed to spend the time to understand.
Thank you for answering the question.

BTW the original question assumed a conductor was attached at appropriate points. I'll make that more clear next time

For the record, though, you can't assume that everyone here is going to be a graduate or Ph.D, then be surprised when they don't know everything there is to know about the depths of the specific area in which they ask a question. Doing so, and responding negatively to them because of it, will only alienate people, which I don't believe is your purpose. There will be the occasional high school student, like myself, who can't comprehend everything they read. Solution: ask someone on an appropriate forum, with the expectation that they won't be a dick about it.

Once again, though, thank you for answering my question.

13. Originally Posted by pippinj
Doing so, and responding negatively to them because of it, will only alienate people, which I don't believe is your purpose.
You will be hard pressed to get him to lighten up, or change his attitude. The other day I visited the site to read the new posts, I hadn't done in quite some time. About half of the top 10 posts had been reduced to pointless exchanges involving Dr Rocket.
"you two jerks"
"gibberish"
etc etc etc

It is a bit tiresome, especially the last week or so where it seems to have got worse. Criticism can be achieved without purposefully invoking anger in people. Keeping crap threads alive with what is essentially a slagging match is another trademark. I've seen a few young people visit the site to learn and are belittled, humiliated or insulted within their first thread.

Yes some people are lazy, Yes some people think they have something sussed out when they don't, yes there are some idiots on this forum, yes it can be frustrating, but treating everyone with the same "your an idiot" attitude until they prove otherwise is not the way someone should conduct themselves on a forum.

He is very smart and has contributed a lot, but the attitude could do with a lot of improvement. Although it makes for entertaining reading sometimes.
I think his motto is "Clown until proven Scientist". If you stick around, you will get used to it.

14. pippinj,
congratulations on hanging on in there till you got the answer. I will agree with Dr. Rocket on one point: reading is an active process. I have found learning generally to be a painful process. If it is not, then whatever I am learning is probably of low value, or merely factual - it contains no concepts. It is concepts that are important and to take these on board does require blood, sweat and tears. Dr. Rocket's approach certainly helps to generate those. :wink:

15. harvestein and Ophiolite, thanks for the encouragement. I'll be better prepared next time. :wink:

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