From: SFPhysics@aol.com
Date: Fri Nov 22 2002 - 01:06:11 PST
From: SFPhysics@aol.com Message-ID: <18c.11976f46.2b0f4d83@aol.com> Date: Fri, 22 Nov 2002 04:06:11 EST Subject: Metered Pressure & Voltages
<< Subject: Meters
> From: "Art Fortgang" <afortga@yahoo.com>
> Date: Thu, 21 Nov 2002 10:39:56 -0800 (PST)
> The chem teacher at my school asked me if there is a
> meter that can be put into a vacuum chamber to display
> the pressure?
> He also wanted to know what would be best meter to use
> to find small voltages generated making a battery.
> Any suggsetions??
> Thanks, Art
>>
Greetings Art:
I used an old aircraft altimeter in a bell jar to show that when air was
removed it was the same as going up in altitude. An auto altimeter will do
the same with less theatrics of having the hands on the dial go around. A
barometer will work within its range (going over the range may permanently
damage sensitive mechanical instrumentation). Then you could use the
opposite tact which I have done to measure air pressure. Completely seal a
small vessel to a pressure meter. Pump the air out of the bell jar and the
pressure meter shows a reading until you get to 760 mm Hg, 14.7 PSI, or
wherever the atmospheric pressure is on the range of the meter. As the air
is removed around it the meter will show a pressure. A small balloon that
has only a bit of air left in it will expand to show the lowering of
pressure. Now if you are looking for a real vacuum meter, yes, there are hot
wire meters that are not cheap, thermocouple meters that are not cheap,
ionization meters that are not cheap, etc. With some electronics background
you can convert a sphygmomanometer (blood pressure gauge) as sold in stores
to allow the pressure sensor to show the internal pressure. A "U" tube
mercury manometer can be used if you aren't worried about the mercury. It
all depends on how accurate the
measurement need be.
As for measuring Voltage, any meter with very high input resistance that will
not load down the smallest chemical cell may be used to show potential
(Volts) generated. My students made simple cells using aluminum foil,
blotter paper saturated with vinegar, and old 97% solid copper pennies to
make cells first. Then they piled them on top of each other to make a
Voltaic Pile for more voltage. Great fun! Later they were encouraged to try
different metals provided in the exploration packet. It is a good hands on
intro to half-cell potentials. I would recommend Harbor Freight Tools #30756
Digital Multimeter now on sale until December 2nd, for unbelievable price of
$3.99 each. It will allow you to get a reading.
Hope that helps,
Al Sefl
Not a stockholder in Harbor Freight Tools... ;-)
This archive was generated by hypermail 2.1.3 : Mon Aug 04 2003 - 16:18:08 PDT