How clocks show Time?— For kids

A simple explanation of how quartz and atomic clocks basically work!

Hello, kids out there! Hope you guys are doing good :)

The common terms we hear around us are ‘It took a lot of time’, ‘Time’s up’, ‘What is the time?’, ‘It’s time to sleep’ and many more conversations related to time. And, as kids, we love to wear colorful wrist watches and sure each of us has a collection of few watches matching each dress. Have we ever wondered how wrist watches show the right time? Here is a simple explanation to that.

What is there inside a watch?

Obviously we need a battery cell to keep the watch alive. But why is the battery for? Here’s the answer. The battery cell provides energy to a quartz crystal.

Why does a quartz crystal need energy?

Well, we all know the basic physics concept of oscillation. Any bells ringed? Yes! The same concept of the pendulum clocks where the term oscillation connects well. A complete oscillation of a pendulum is one second. So, for every oscillation, the clock counts one second. By this way, clocks show time. But we can’t carry a huge pendulum clocks all day long. We need some other device to count one second instead of the pendulum. So, scientists came to a conclusion, why not crystals? Crystals can be given some energy and can be oscillated. Here, oscillation is not the literal to and fro swing motion. The quartz crystal will move to a higher energy and come back to lower energy when power is not given. This movement from lower energy to higher energy, and again to lower energy is kind of oscillation. This oscillation counts the seconds. Meaning, one oscillation per second. And this vibrates in the same frequency. This way, the clocks show the time, but not the right one all the time!

How does the time go wrong in a quartz?

A crystal’s frequency of vibration changes with respect to temparature and pressure. That’s why in few countries like US, UK, they keep their watches and clocks changed during summer and winter.

Is quartz clock enough for all applications?

Quartz watches are far enough for common use like how we use our watches to check time. That small deviation in frequency is not a big deal for us. But, there are few places where even a deviation of one second keeps hundreds of miles apart. Can’t believe? Yes, in space, a difference of one millisecond causes 300 miles difference in something traveling at the speed of light. So an accurate clock is required to measure time of traveling signals and spacecrafts.

What’s special in atomic clocks?

An atomic clock is just an add on to a working quartz crystal. The frequency deviation in quartz crystal is corrected using atoms. It’s as simple as that. But how?

How atomic clock works?

Atoms have electrons placed in their energy levels. The electrons move to the next energy level on application of energy. In atomic clocks, we have a set of atoms configured to be excited upon appliying certain energy. If the same energy is applied all the time, then the same set of atoms get excited. If less energy is applied, then less number of atoms get excited and if more energy is applied, then more number of atoms get excited. So this can act as a measure of how much energy is applied. The frequency of the quartz is applied to this set of atoms. whenever therer is a frequency deviation in the quartz crystal, it will affect the number of atoms getting excited. This way, we can know how much frequency deviation occurred. Then, by using a corrective action, this deviation is corrected in the quartz.

So basically, atoms are used to correct the frequency deviation of a quartz crystal, thus helping in maintaining accuracy.

Atomic clocks are widely used for space applications, spacecrafts, gps transmitters, satellites etc.