The waves of wavelength 6000 Å emitted by any atom or molecule must have some finite length whichis known as coherence length. For solution light, the length is 2.4 cm. what is the number of oscillations for this length?

Options

A. `4xx10^(8)`
B. `4xx10^(4)`
C. `4xx10^(6)`
D. `4xx10^(5)`

Answer

B

Explanation

For solving this, we must know temporal coherence. When an excited atom goes to the ground state, light of definite wavelength `(lamda)` is emitted. The duration of this transition is of the order of `10^(-9)` to `10^(-10)`s and this time is known as coherence time `(tau_(c))`.
the length `L=ctau_(c)` is known as coherence length and the number of oscillations in coherent length is given by
`N=(L)/(lamda)=(0.024)/(6000xx10^(-10))`
`therefore N=(24xx10^(-3)xx10^(7))/(6)=4xx10^(4)`