Question

One second is defined to be equal to:
A. 1650763.73 periods of krypton clock
B. 652189.63 periods of krypton clock
C. 1650755.73 periods of cesium clock
D. 9,19,26,31,770 periods of cesium clock

Answer 1

Hint: Recall that every unit in the SI system has a proper definition so as to universalize them. One second is the unit of time in the international system (SI) of units. Find out which among the above given options correctly defines one second. Also, define what you mean by 1 period in that clock.

Complete step by step answer:
Taking measurements is an inevitable part of our everyday life as well as in every field of science. We have been using various systems of measurements since time immemorial. Along with the evolution of technology we have seen developments in methods used in making these measurements. As years went by, we saw a need to universalize these measurements. By the system of measurements we mean various unit systems that we use to make these measurements.
In the present day we have accepted the international system of units, abbreviated as SI as the standard measurement. That is, a measurement made in SI means the same over the whole globe. For example, we use meters for length, kilogram for mass, amperes for current, etc. There are fundamental units and derived units. In the SI system we consider 7 basic/ fundamental quantities and then we derive the units for the quantities that are derived from them. Mass, length, time, current, amount of substance, luminous intensity and temperature are the 7 fundamental quantities. Each one among them has a unit under the SI system. Each of these units also has a proper definition.
We are supposed to find the definition of one second in this question. One second (s) is the SI unit of time. It is defined as 9,19,26,31,770 periods of cesium clock. By giving a definition like this to one second we are universalizing the unit of time, that is, when we say one second, it means the same all over the universe.
Let us see what is meant by a period of cesium clock. It is defined as the time taken for the cesium atom to vibrate between two energy states. We know that electrons in cesium atoms, when exposed to a certain frequency, get vibrated between energy levels. So, 1 second is defined as that time interval in which an electron in a cesium atom jumps 9,19,26,31,770 times between different energy levels when exposed to radiation of particular frequency.

So, the correct answer is “Option D”.

Note: Before cesium clock, scientists have used crystal quartz clock and even mechanical pendulum to define one second. However, both of them ended up showing errors and that is when the SI system came into picture with a better definition using cesium clock. Since then cesium clock (atomic clock) is known as the accurate method.