Atomic Clocks.

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Atomic Clocks

Name: Wong Yun Sheng Calvin (2O/23)

As pictured above, a scientist stands over a NB-5 atomic clock.

How do atomic clocks work?

Atomic clocks measure time by the frequency of radiation emitted by an atom or molecule when it makes a transition between two energy states. An atomic clock measures the frequency of electromagnetic radiation emitted by an atom or molecule. Atomic clocks are extremely precise and are used to keep universal time—the international basis for establishing legal and scientific times and for setting all public and private clocks worldwide.

When an atom or molecule moves from one energy level to another, a specific amount, or quantum, of energy is absorbed when jumping to a higher energy level or emitted when falling to a lower energy level. The amount of energy absorbed or emitted depends on the difference between the energy levels. The atom or molecule emits energy in the form of electromagnetic radiation and the wavelength and frequency of the radiation depends on the amount of energy released by each transition between energy levels. Because the atom or molecule can only emit or absorb a specific amount of energy, the radiation emitted or absorbed has a regular frequency. A counter in the atomic clock keeps track of each cycle.

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Atomic clocks determine the frequency of an atom or molecule’s transition in one of two ways. An active atomic clock induces a group of atoms in an elevated energy state to drop to a lower energy state, measuring the frequency of radiation emitted by the atoms. A passive atomic clock exposes a group of atoms in a lower energy state to electromagnetic radiation with changing frequency. When a majority of atoms jump to the next energy level, it signals that the correct frequency has been achieved.

Most atomic clocks in use today are passive cesium clocks. The United States National Bureau of ...

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