Question

One second is equal to

Answer 1

Second:

Duration of a second

1. A second is defined as the time it takes to see exactly $9,192,631,770$ cycles of radiation produced by the transition between two levels of the $Cs-133$ atom at sea level.
2. We currently use the $Cs-133$ atom because its resonance levels make it possible to manufacture very high-precision clocks.
3. Atomic clocks are devices that are designed to measure the exact length of a second, which is the fundamental unit of modern timekeeping.
4. The second was originally defined as $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$86400th$}\right.$ of a day but in reality, this is difficult to nail down to high precision. This is because $1day$ consists of $24hours$ and $1hour$ consists of $60minutes$ and $1minute$ consists of $60seconds$.
5. So, $Numberofsecondsinaday=24\times 60\times 60=86,400seconds$.
6. Previously, the second was known as the "second minute", meaning the second minute, a small division of an hour.
7. The first division was known as the "prime minute" and is equivalent to the minute we know today.

Thus, one second is equal to $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$86400th$}\right.$ of a day.