Frequency vs Intensity

The frequency heard by the listener can be calculated using Doppler effect . As the train approaches the man, the frequency observed by the man increases.

Intensity is rate of transfer of energy per unit area. Since power is rate of energy transfer, intensity is equivalent to power transmitted per unit area

$\text{Intensity} = \frac{\text{Power}}{\text{Area}}$

Consider a sphere with the source at its center. Since power transmitted is constant and the surface area of the sphere is $4\pi r^2$ ,

$\text{Intensity} = \frac{P}{4\pi r^2}$

We see that the intensity of sound heard is inversely proportional to the square of the distance between source and listener.

Therefore as train approaches the listener, the listener observes that both frequency and intensity of sound increases.

Hey guys have u ever been on a railway station? If u have encountered a train coming to u , u experience louder & un tolerable noise when train rushes toward u.It means its intensity increases. Now FREQUENCY What happens to it?It also increases. If sound come from too far it encounter more particles (remember sound is a mechanical wave) hence it loses its energy(intensity) and identity (frequency ) with each interaction. I HOPE IT HELPED U! CHEERS! !!