Date: Mon, 25 Oct 2004 09:51:03 -0400

Author: Michael Timmins

Subject: RE: beaker breaker


On Sat, 2004-10-23 at 17:33, Richard Berg wrote:
> Folks,
> I need to purchase a new oscillator, power amplifier, loudspeaker,
> microphone, oscilloscope, strobe, TV camera, and monitor to fabricate a
> beaker breaker apparatus for a group of Taiwan physics people to use for
> their 2005 Year of Physics celebration. I know what we have in ours and,
> lamentably, most of it is obsolete.
> So for those of you who made a recent one using modern equipment, what do
> you use?
> 1. oscillator: Is the Pasco $200 generator sufficient, or do you need more
> tuning resolution, for example, in the digital function generator? Seems
> a bit extravagant, but may be necessary to get the resolution without
> loading and changing frequency.
We used to use an old HP model 200CD which worked fine, but now use the
digital pasco function generator so I can tell people before class that
the resonance is at xxx.xx.
> 2. amplifier: I presume that a black box power amp is necessary. Do you
> have one with a simple volume control?
QSC Power Amplifier 3.5 150W output has only an on switch and volume
> 3. loudspeaker: We used a high-power horn driver. I presume that the one
> we used is good - it has to take up to 100 watts or thereabouts so that
> it will last forever.
same here
> 4. microphone: We need a microphone to pick up the sound of the resonant
> beaker. Will an ordinary microphone and scope work, or do you need some
> greater output (say a microphone for oscilloscope or a little amp between
> the mic and the oscilloscope) so that it will work with an ordinary
> oscilloscope?
Radio Shack el cheapo lapel condenser mic.
> 5. oscilloscope: I presume the basic Pasco 20-MHz scope will do the job -
> perhaps with an ordinary dynamic microphone. Seems a bit extravagant -
> anyone have a less expensive but reliable alternative?
Once you get the hang of it, a folded piece of paper is reliable. but we
like to show the wave form at the same time during the demo. I bet any
one of those free software oscilloscopes which look at the sound card
input on a computer would work great. I never tried it, but how about
replacing the mic and scope with a portable db meter?
> 6. stroboscope: It looks like the Pasco version is too slow - 300 Hz,
> compared with about 900 Hz for the vibration rate of the beaker. Has this
> worked out for anyone, or do you have an alternative?
> 7. video camera: I presume that the most basic one with a standard lens
> will work.
It's nice if the camera has a "long exposure time" setting to prevent
beating with the strobe.
> 8. monitor: A basic B&W monitor - perhaps about 17-19 inch so it can be
> seen by a medium lecture class. Can also send the signal to a projector.
> Any suggestions?
We have a big tv for the scope and projector for the glass. In a small
class, we hand out goggles for a close up view whenever possible.
> Thanks in advance for your insightful comments.
> Dick
> ***********************************************************************
> Dr. Richard E. Berg, Professor of the Practice
> Director, Physics Lecture-Demonstration Facility
> U.S. mail address:
> Department of Physics
> University of Maryland
> College Park, MD 20742-4111
> Phone: (301) 405-5994
> FAX: (301) 314-9525
> e-mail
> ***********************************************************************
Mike Timmins
University of Virginia
Acadamic Support Supervisor

phone: (434) 924-6800
mail address:
382 McCormick Rd
Charlottesville, VA 22904
From Mon Oct 25 07:11:09 2004