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Re: [Phys-l] glassware needed

While we are on the topic of issuing (unwanted?)
specific heat experiment advice,
let me too pitch in.

Volumetric measures for the test fluid are not a particularly good example.
Weighing before and after are likely to give much more accuracy for the buck.
Taking the temperature rise with a thermocouple to a DVM is another good example.

The idea of using a thermally benign container is so cheap, so effective that
it is hard to imagine using another way: expanded polystyrene is the name of that game,
with a similar cover for the cup to reduce evaporative loss. I have also
bought thermos flask liners which would provide plenty of thermal resistance,
at the cost of some thermal capacity.

It would be better not to take the rated power dissipation of a heater on trust:
a wattmeter is now so within reach that it would be a good accessory.
This would enable a TRIAC dimmer to moderate the power, and stretch
the test period as desired. Power tool (even light switch) power dimmers do not run high.

There is a range of heaters intended for aquarium applications: 25,50,75,100,150 W
etc. My cursory search of these turned up in-line heaters too: this is a preferred
way of avoiding some systematic errors. TempIn TempOut, mass output, watts

Happy New Year!

Brian Whatcott

At 12:58 PM 1/1/2009, you wrote:
Why not just go to Wal-Mart and buy some straight sided drinking glasses? Cheap!

Bob at PC


From: on behalf of Anthony Lapinski
Sent: Mon 12/29/2008 12:34 PM
Subject: [Phys-l] glassware needed

Happy holidays everyone!

I want to do a lab activity using a small immersion heater and a beaker of
water. However, our beakers all have the usual sloped tops with a spout.
The clip on the immersion heater is meant for a coffee cup with straight
sides, and does not secure well to the beaker. It will fit on a tall
graduated cylinder, but then it is difficult to mix the water to get a
good temperature readings.

So I am looking for a straight sided beaker (graduated if available) to do
this experiment. I searched unsuccessfully on the interned, but only found
straight sided plastic beakers and jars. Nothing made of glass and

Does anybody know of a source/company for what I need? Thanks!

Forum for Physics Educators

Brian Whatcott Altus OK Eureka!