Which statement best captures the passage’s main idea?

Atomic clocks steer an electronic oscillator toward a reproducible atomic transition, while controlling and comparing sources of error. (The passage follows the reference, feedback loop, corrections, and comparisons that make precise timekeeping possible.)

Why does the clock need a feedback system?

The electronic oscillator can drift, so the atomic response is used to steer it back toward resonance. (The response reveals whether the microwave signal is off frequency, allowing repeated adjustment of the oscillator.)

What does “resonance” mean in this passage?

The frequency region where the applied microwaves most strongly produce the chosen atomic transition (Near resonance, more atoms make the desired energy transition, providing the response used to tune the oscillator.)

What does the passage say laboratories may correct for?

Relativity when height or motion matters (The third paragraph names relativity alongside uncertainty estimates and controls for physical disturbances.)

A Clock That Listens to Atoms: Level 5 Reading Comprehension Questions

An atomic clock does not count atoms, and its timekeeping does not depend on radioactive decay. It uses a regular transition between energy states inside atoms as a reference. For cesium-133, the official definition of the second is tied to 9,192,631,770 periods of radiation associated with one particular transition.

The practical clock begins with an electronic oscillator that produces microwaves. Cesium atoms pass through or interact with that signal. When the microwave frequency is slightly wrong, fewer atoms make the desired transition. When it is near resonance, the response grows stronger. A feedback system continually adjusts the oscillator toward the atomic response. Electronics count the stabilized cycles and turn them into seconds.

The atoms are therefore a reference, not a tiny display with hands. Real devices must control magnetic fields, motion, collisions, temperature, and electronic noise because these can shift a measurement. Different clock designs reduce different disturbances. Laboratories compare several clocks, estimate uncertainty, and correct for relativity when height or motion matters.

No single instrument silently defines time for the world. National laboratories compare standards, and international organizations combine measurements into shared time scales. Atomic clocks support navigation, telecommunications, power networks, and scientific tests because distant systems can coordinate against a carefully measured rhythm. Their strength comes from a loop: physics supplies a reproducible transition, engineering keeps an oscillator aligned with it, and comparison reveals remaining error.

Comprehension questions