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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.
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!