If glass expanded just as much as alcohol with increasing temperature,
thermometers wouldn't work: the increasing size of the thermometer bulb
would accommodate the increasing volume of liquid. The thermometer
depends on there being a difference between the response of the two
materials, and then finds a way to magnify it so that we can see it.
Aluminum foil and transparent tape also differ in their response
to changes in temperature.
We can show this as follows:
Find a piece of aluminum foil that is smooth and flat (if one
is a little rumpled, you can smooth it and flatten it by rubbing it
on a table), about 2.5 cm x 15 cm (1" x 6"). Tape it to a smooth surface
(a table top), so that
it is stretched flat and can't move. It isn't necessary to use a lot
of tape -- this is just to hold the foil in place while we do the
next step.
Now stick a piece of tape to the foil (running the length of the
foil),
by first sticking the tape down at one end, and
then stretching it slightly as you smooth the tape into place.
Scribble on the tape with a marker, so that it is dark colored.
This will make it more sensitive to bright light.
Now unstick the foil from the table, and trim away the foil that
doesn't have tape stuck to it.
As you trim, the tape will curl the foil (because
you stretched it), and the result will be an
arch or ring or coil.
Stand the tape arch so that it is bending away from the table top
(perhaps taping the bottom of the arch so that it stays in place),
and place it
under a bright incandescent lamp (or even a flood light, if you
have one) or in direct
sunlight, and turn the light off and on,
or cast a shadow on it. (If you do this outdoors, it might
be helpful to put the tape arch in a box or a large glass jar to
protect it from the breeze).
The tape and the aluminum foil
both expand, but by different amounts, and this causes the arch
to open and close a little bit. Which expands more, the foil or
the tape?
The device you have made is not a very reliable thermometer, because
it's probably sensitive to
humidity as well as temperature, and the breeze blows it around. The marker solvent may
dissolve into the tape, with the result that the properties of the
tape are changing during your observations.
However, using different kinds of metal instead of tape and foil solves
these problems.
There is a very useful kind of thermometer that works this way, called
a bimetallic coil.
There is one in your kit.
The tape and the aluminum foil
both expand, but by different amounts, and this causes the arch
to open and close a little bit. Which expands more, the foil or
the tape?