What is the SI unit for time?

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Build your vocabulary for the IGCSE Coordinated Science Exam. Study with flashcards and multiple choice questions, each with hints and explanations. Prepare for success!

Multiple Choice

What is the SI unit for time?

Explanation:
Time is measured using the SI base unit for time, the second. The second is defined very precisely as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the cesium-133 atom in its ground state. This definition gives a stable, universal standard that can be reproduced anywhere in the world, which is why clocks and timing rely on it. Other options measure different quantities—length, temperature, and mass—so they don’t describe time. Derived units like minutes or hours exist, but they’re just larger multiples of the same base unit.

Time is measured using the SI base unit for time, the second. The second is defined very precisely as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the cesium-133 atom in its ground state. This definition gives a stable, universal standard that can be reproduced anywhere in the world, which is why clocks and timing rely on it. Other options measure different quantities—length, temperature, and mass—so they don’t describe time. Derived units like minutes or hours exist, but they’re just larger multiples of the same base unit.

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