It is simple to
demonstrate the piezoelectric property of quartz and show how the size and shape of quartz
effects its vibration. Make two jellies of slightly different size and see how the
frequency of their vibrations compare.
Quartz Clocks
Not all watches and clocks have gears, pendulums or cogs. In the 1930's and 1940's watches
and clocks started to use very thin wavers of quartz to measure the time. Passing an
electric current through the quartz makes it vibrate. This is called the piezoelectric
property of quartz, and is how a watch tells the time. The watch literally counts the
number of vibrations the quartz makes, does a simple calculation and works out what a
second is.
The vibration of quartz is affected by the size and cut of the crystal, so the accuracy of
the time depends on how well the quartz is cut. No two quartz crystals are exactly alike
with the same frequency, which limits the accuracy of these clocks. Their performance has
been surpassed by atomic clocks that measure the vibrations of atoms.
 Materials
2 packets of jelly
2 jelly moulds (one small, one large)
2.5 pints of water
2 plates
Spin drier/washing machine on spin cycle!
1 tea-towel
Make two separate jellies, but make them different consistencies by dissolving the jelly
chunks in different quantities of water. Mix one packet of jelly with ? of a pint of water
for the small jelly and mix the remaining packet of jelly with 1½ pints of water for the
large jelly. Place the jellies in the fridge and allow to set over night.
When set, dip the jelly moulds into hot water for 30 seconds and turn out each jelly onto
a plate, refrigerate again for one hour. When the jellies are completely set, remove them
from the fridge and place both plates on a tea-towel, on the surface of a spin drier or
washing machine. Set to spin cycle (take care that the plates don't wobble off the
vibrating surface!) and watch the jellies vibrate.
You should notice the larger jelly wobbling slower than the smaller jelly. The difference
in the frequencies of their vibrations illustrates how quartz crystals of different sizes
produce different vibration frequencies. |
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