Question: what type of physics do u do ?

Hannah Collingwood answered on 13 Mar 2019:

A lot of the work I do is directly related to clocks. When most people think of a clock, they think of a dial with hours spaced equally around its face (or maybe a digital watch) but the types of clocks I work with need to be able to measure much more precisely than seconds.
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There are many different types of clock, but they all have the same features: an oscillator, a reference, and some way of reading it. Let’s look at a few examples:
– A grandfather clock has a pendulum that swings (the oscillator) and the time is shown on the clock face. The reference is the Earth’s rotation: there are 24 hours in a day.
– A digital watch will have a quartz crystal that vibrates (oscillator) and the time will be displayed on the clock face. The reference is also the Earth’s rotation.
– Caesium clocks use the transition of electrons in caesium to create microwaves (oscillator). The reference here is the caesium atom.
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What makes a good clock? This depends on what you need it for, but the best clocks will have an oscillator that can give very reproducible oscillations, where the frequency is the same every time. It is also useful to have clocks that have very small frequencies, which means that it is much easier to count fractions of a second.
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The type of clock you choose will depend on what you need it for. For everyday use, quartz clocks are fairly cheap and have pretty good accuracy. However, you might find yourself needing to adjust the time periodically as quartz isn’t very stable over very time periods of time. The clock in your phone will use signals from satellites or other networks (including WiFi) to make sure it keeps the right time. If it doesn’t have a connection, you will see the clock start to drift too.

Sometimes much better clocks are needed. These tend to be much more expensive but mean that the clock will be able to measure much smaller time increments and/or will drift less noticeably. This is where caesium clocks are used, but there are other types of atomic clock too.