Detecting changes in temperature without a thermometer
In a number of the activities* where an increase of temperature
takes place, it can be felt with your hand. These are Activities I-3B, I-4C,
I-4C Further Study, I-5A and I-10.
(* The classroom activities referred to here are those described
in Peace Corps ICE manual M10, Preserving Food by Drying: A Math-Science
Teaching Manual.)
In several other activities, the increases in temperature can be
noted the same way, but it would be desirable to improve both measuring skills
and understanding of the situations by making a somewhat more quantitative
measurement. The approaches suggested here apply to these activities: I-5B, I-7,
I-7 Further Study, I-8B, I-11A, I-11B and II-2.
In the Further Study following Activity I-3A, a laboratory
thermometer which can measure temperatures up to 100 C is needed. This is a
difficult requirement to meet with improvised temperature measuring devices, but
perhaps you can invent one or locate an existing design that is easy to make and
works well. If you do, please communicate it to the Information Collection and
Exchange office. Also, please let us know about your successful or unsuccessful
attempts to measure temperature in any of the lessons.
In many industrial applications, temperatures are measured using
pieces of material that melt at known temperatures. For example, in Activity
I-7, three tiles are placed in the sun. They are all horizontal. One is black,
one is earth colored, and the other one is white. On each tile, you could put a
piece of margarine and a piece of wax. Whether both of these melt on each tile,
and how long it takes could be noted. Maybe in your locality, both of these melt
too easily. Can you find another material that melts at a higher temperature?
The following device can measure small and medium changes of
temperature.
Fig. 68
The air trapped in the tube expands as the temperature rises.
Experiment with the size of the air space. A small air space gives less
sensitivity, but a higher temperature can be measured without the water spilling
out the end of the tube. The range has an upper limit near the boiling point of
water because too much water vapor forms in the air space. Positions along the
tube can be marked, or it can be glued to a piece of paper, pasteboard, plastic
or wood, and that can be marked.
The following device is useful for measuring relatively small
changes in temperature. Air in the body of the pen expands to move the colored
water. Air must be free to leave or enter the tip. Water getting in it will
impair its operation.
Fig. 69
All connections must be sealed, including the small hole on the
side of the pen. When the air is warmed and expands, it pushes the colored
water. It must not escape elsewhere. The whole device is sensitive to change of
temperature. Either the whole thing should be put in the place where temperature
is being measured, or the same length must be used for all measurements which
are to be compared. It also responds to your warm fingers, and thus must be held
some other way.
As you can see, these devices have some merit, and we are
anxious to hear of your efforts to use them However, they also have limitations.
Perhaps they can be adapted in some way to become better.
The conditions of measurement in the various activities are as
follows:
