Timekeeping. How could such a mighty power be exploited by a device as diminutive as a quartz wristwatch, to a remarkable degree of accuracy? Today we will break open one of said watches (through writing, of course), and see what lies inside.
What is quartz? Besides being an excellent word to play in Scrabble, quartz is the second most abundant mineral in the Earth’s crust, after feldspar. It is often used in jewellery as it has quite a nice shiny appeal to it.
But as much as we like shiny stuff, we’re here to employ one of its other exclusive properties, piezoelectricity. A piezoelectric crystal builds up electric charge when pressure is applied to it, so piezoelectric materials are often used in various electronic sensors. This property was first discovered in 1880 by French physicists Jacques and Pierre Curie.
This process also works in reverse. When an electric current is applied, the crystal will oscillate, and this is the property of quartz that we want to exploit. When you apply a current through a quartz crystal, it oscillates at its resonant frequency of exactly 32768 per second, or 215.
This number does not change with gravity, i.e. it would not change whether you were at sea level, or on the summit of Mount Everest, or in the International Space Station. This is a great advantage over the previous common timekeeping device, the pendulum. Quartz does undergo very small changes in size with temperature, but this is rarely significant with regards to the temperature changes on Earth. So quartz is looking very promising as a timekeeping device to replace the pendulum!
The quartz is typically contained within a tiny metal container inside of the watch. The battery powers a microchip, which sets the quartz to oscillate at its precise frequency. The microchip then detects the mechanical oscillations and converts them into electrical pulses. These pulses turn an electrical motor, which turns gears, which turn the hands that we see sweeping clock faces and allows us to keep track of time.
As you can see from the image, this whole mechanism, electronics and all, is able to fit into the size of your wrist. Although the first quartz clock was built as early as the 1920s, it has taken many, many decades and much progress in solid-state electronics to reduce them to this size. (Don’t open up your own watch though! They’re very delicate and may break.)
Then there’s the super high-tech atomic clock which is far more precise and reliable than a quartz clock. However that may be a post for another time…