# Search results

1. ### Ultrasonic Standing Wave Suspension could the transducer support itself?

I fear you overlooked something. They state clearly : "The first system was able to lift a weight of 3 kg using an electrical input power of only 16 W. Based on the surface area, a lift capacity of 11.5 kN/m2 was reached." 11500/30 ~ 380; 16W* 380 ~ 6000W, so even assuming peripheral losses...
2. ### Determining Compass Bearing from Resultant Angle

Maybe a nitpick, but: Are you sure you want/need to add wind speed and (water) current? (I assume water because of "current" and the values you use)
3. ### Schools Oil mechanics universities

Not Germany, but have a look at http://en.wikipedia.org/wiki/University_of_Leoben
4. ### Surface area of a bulb filament

There are special lamps for precision measurements in photometric, for example this one: http://www.pyrometer.com/ribbon_lamp.html I´ve found one source for emissivity of tungsten here: http://www.monarchserver.com/TableofEmissivity.pdf [Broken] If you expect high accuracy in...
5. ### Gravitational Vortex Power plant

I replied to a similar question here https://www.physicsforums.com/showthread.php?t=520878 about two years ago. Maybe i was a bit unfriendly, but things haven´t changed much since then. Most of the technical information I linked to is in German, so you´ll have to translate.
6. ### Is it possible to power a freight train with an animal motor?

As jtbell points out, some of the first railroads started with animal traction, at least in Europe. http://en.wikipedia.org/wiki/Saint-Étienne_to_Andrézieux_Railway http://de.wikipedia.org/wiki/Pferdeeisenbahn_Budweis–Linz–Gmunden (sorry, no English version available). Steam locomotives soon...
7. ### Conversion of Voltage into Radiation counts

You might try evaluating the output of a proportional counter using a very sophisticated digital storage oscilloscope, but that would be a lot of effort and probably not worth it. http://en.wikipedia.org/wiki/Proportional_counter
8. ### Vacuum possible from Gaede mercury pump from 1913.

I used a mercury diffusion pump (quite) some time ago. With a bit of heating the vacuum got down below 10-5 torr. Of course there was a cryotrap between the pump and the vacuum vessel (liquid nitrogen).
9. ### Power on/off bi-color led circuit?

If this is about safety (outside of a purely experimental setting) you better check the codes and regulations applicable. Probably there are a lot of them. You will find that there are standard circuits designed to comply with the codes. Just find out and use them. Don´t try to cut costs or to...
10. ### Collimating incoherent light emitted by a LED

You´re perfectly right about the pinhole. The standard way of producing a parallel beam used to be: Use a lens to produce a (reduced) image of your light source onto/into a pinhole. Try to capture as much of the light as possible. On the other side of the pinhole, use a lens to produce your...
11. ### Output buffer for audio

In theory you are correct with a 20db conversion factor. But it applies only for a point source, far field conditions and negligible influence of the measuring microphone, and you cannot assume all of that. You can only use the 20db as a sanity check. Yungman is essentially right: you are...
12. ### Output buffer for audio

A headphone/earphone driver needs to produce sound pressure in the ear only, so it is tested on an ear simulator (a small, short tube, you can find the details in the datasheets in the links you gave). A "normal speaker" is expected to produce sound everywhere around it. Apparently this needs...
13. ### Output buffer for audio

The speakers you linked to are for headphone/earphone use, forget about them. (The db numbers don´t mean the same as in normal speakers). You need size for a decent midrange, don´t go below 30mm diameter if you can. (A cordless phone phone I repaired a few weeks ago has a 36mm speaker for...
14. ### Magnet on fridge

Quite a few deep freezers heat the sealing surfaces to prevent buildup of ice. But I´ve never heard of one using electromagnets. As vk6kro said, the magnet in the door seal is strong enough. I disassembled seal once and found a strip of magnetic material all along the seal.
15. ### Cheap Hydrostatic Testing Chamber

You might be interested in this.
16. ### Constantly record voltages and subtract voltages

Modulating the laser is a good idea, just use a lock-in-amplifier to get your absorption signal. (In the long run it may even be more economic than designing, building and testing some "homebrew" solution)
17. ### How are nodes and antinodes added to harmonics of open air columns?

In many woodwind instruments there are holes for changing the effective lenth (changing the position of the final antinode) and one hole (sometimes two or three) for "adding an internal antinode". These holes are called register holes and on more complicated instruments they are opened by caps...
18. ### Sound/accoustics - guitar string question

sophiecentaur, your statements about the (extent of) anharmonicity of overtones are a bit surprising to me. I´d like to learn more about it; so could you please point out your sources? Edit: I know about the anharmonicity of piano strings, so no need to bother with that.
19. ### Contact sparks

The capacitor discharge method will only work if you open the contact while current is flowing. You need a drive for that. (and some kind of synchronization) If you are only after a spark: why don´t you use a piezo gas lighter? Much simpler than everything we discussed so far. I also suggest...
20. ### Contact sparks

I worked with a test rig for circuit breakers as an intern long ago. I don´t remember wether it was pneumaticlly driven or spring loaded; the electrical part was a capacitor discharge triggered by a SCR. You could scale that down for "household use". Triacs and SCRs have pretty good pulsed...
21. ### Contact sparks

There is a kind of contact spark that does not need very high voltage: When a metallic contact is opened (while current is flowing, of course) there is a spark. Designing (high power) switches has a lot to do with quenching this spark as fast as possible. There may be limits to this effect, but...
22. ### Harmonics in music

There are at least three topics here: In an amplifier you want the output signal to be as similar to the input as possible, (except for more amplitude). One way of testing the quality of an amplifier is putting in a pure sine wave and measuring the overtones it produces. (often called total...
23. ### Scientific principles involved in Pan flute

To my way of thinking a Helmholtz resonator is something in which the "Helmholtz resonance phenomenon" happens, not only the devices Helmholtz used. A blown bottle is a Helmholtz resonator and you can tune it by changing the amount of water in it. This may be what your friend was talking about...
24. ### Scientific principles involved in Pan flute

No, pan flutes do not work like a Helmholtz resonator. Can you please explain what the water is for in a pan flute? I´ve not heard of this before. There was a thread about pan flutes here: https://www.physicsforums.com/showthread.php?p=3806786 You´ll find formulae and references there.

26. ### Elastic collisions between multiple bodies

http://en.wikipedia.org/wiki/Restitution_coefficient CoR = 1 is the definition of an elastic collision.
27. ### Elastic collisions between multiple bodies

You will have to apply momentum conservation (momentum is a vector, so angles will come into this) and energy conservation to solve this. And you´d better start with two particles. I did not know that Newton posited a "law of restitution".
28. ### Laser cutting device to cut paper of few mm from a red laser pointer

This laserplotter is made almost entirely from components cannibalized out of old computers and other electronic devices. May be adaptable to a laser cutter. (It´s in German, though) http://www.heise.de/hardware-hacks/projekte/Laserplotter-1351340.html.
29. ### PNP transistor and argument with my teacher

Your drawings in posts 21 and 25 are perfectly ok, as far as I can tell anything at all.
30. ### PNP transistor and argument with my teacher

I hope i´m not heaping confusion on confusion, but: Kirchhoff can be done in two ways: Voltage drops negative and sources positive or the other way round (see: http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws). And then U=RI and current direction and sign conventions come in.