Re: [Phys-l] glassware needed

[ludwik kowalski <kowalskil@mail.montclair.edu>]

Systematic errors resulting from heat losses (mentioned by Hugh) would  
be reduced significantly if the recorded temperatures were in the  
range between ~10 and ~40 C, for example. Another suggestion is to  
wrap the container with a layer of flexible styrofoam, or something  
equivalent. Corrections for some heat losses can be made on the basis  
of the rate of cooling. A good cover, with a small hole for electric  
wires, could help to further reduce heat losses. With these  
precautions the measured thermal energy gain could be only slightly  
lower than the amount of delivered electric energy.

My suggestion is to divide this activity into two parts--crude and  
refined. The first preliminary result (without additional insolation,  
broader trmperature range and no cooling correction) could be  
discussed with kids before going to the second part. Let them to be  
creative. This old introductory physics topic can be handled in many  
different ways, some more productive than others. Please share  
observations, Anthony.

On Dec 30, 2008, at 7:34 AM, Anthony Lapinski wrote:

> I did. They are small and the water heats up quickly.
>
> Immersion heaters are about 300 W. Use Pt = mcT. In theory, 1 L of  
> water
> at room temp reaches boiling in abut 18 min. A cup of water (about  
> 0.25 L)
> takes around 5 min. I wanted kids to graph temp vs time over an  
> "extended
> period, and then calculate the power of the heater and compare to the
> actual value. I wanted a graduated container to easily measure the  
> amount
> of water.
>
> So far, the Pyrex measuring cup is the best idea. The glass is  
> thick, but
> still works with the clip on the immersion heater. And the markings on
> these 0.5 L and 1 L cups have metric markings. Have not checked heat  
> loss
> errors via the air/glass yet...
>
> Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>  
> writes:
> > I must be something here -- why not use a coffee mug?
> >
> > bc obsessively collects them.
> >
> >
> > On 2008, Dec 29, , at 09:34, Anthony Lapinski wrote:
> >
> > > 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
> > > graduated.
> > >
> > > Does anybody know of a source/company for what I need? Thanks!
> > >
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>
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Ludwik Kowalski, a retired physics teacher
5 Horizon Road, Apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/