The pitch or frequency of the siren of the coming train appears to be increasing because of:

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Big-bang theory

Doppler’s effect

Charles law

Archimedes law

answer is B.

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Detailed Solution

:
Concept: The name of the phenomena is generally attributed to the person who saw the aforementioned incident and came up with the concept. The effect may be observed if there is movement between the sound source and the observer. The optimum approach will be determined by who observed the aforementioned behaviour.
When the source of the waves is travelling in the direction of the observer, each subsequent wave crest emits from a place that is closer to the observer than the previous wave. Because of this, each wave reaches the observer a little bit quicker than the one before it. The frequency rises as a result of the shorter time between successive wave crests reaching the observer. As the waves travel, they "bunch together" because the distance between wave fronts grows narrower. This is due to the Doppler effect.
As a result, it appears as though the train's approaching siren's pitch or frequency is growing.
Hence, the correct answer is option 2.

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