Question

$1ns$ is defined as

• A. ${10}^{-9}s$ of Kr–clock of $1650763.73$ oscillations
• B. ${10}^{-9}s$ of Kr–clock of$6521389.63$ oscillations
• C. ${10}^{-9}s$ of Cs–clock of $1650763.73$oscillations
• D. ${10}^{-9}s$ of Cs–clock of $9192631770$ oscillations

Answer 1

The correct option is D

${10}^{-9}s$ of Cs–clock of $9192631770$ oscillations

Step 1: Definition of $\mathbf{1}\mathbf{}\mathit{s}$

One second is the amount of time in which the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133 atom completes its $9192631770$ periods.

Step 2: Write relation between second and nanosecond

$1ns=1\times {10}^{-9}s$

Step 3: Definition of 1 ns

Now, we can say, one nanosecond is ${10}^{-9}s$ of $Cs-clock$ of $9192631770$oscillations.

Hence, option (D) is correct.