DTTB TransmissionRevisiting “DOPPLER Shift”

Decreased periodHence increased frequency

F= f + f * Vt / Vs

?

Vt

Vs

Vt = Speed of train

Vs = Speed of sound ( constant )

C R C R C R C R

C = Compression

R = Rarefaction

Whistle (f)

Vt

Vto

Vto = Observed speed of train

Vto = Vt * cos ?

?

Vto

Vt

Vto = o

Vto = Vt * cos ?

Vto = Vt

Explanation : While a “compression” of sound is in the air it is followed by another, but closer, aided by the speed of the train.

Period between the “compressions” are unmodified by the speed of the train

Period between the “compressions” are

partially modified by the speed of the train

f = frequency of whistle

F = Observed frequency

F= f + Cos ? * f * Vt / Vs

- for approaching

F= f - Cos ? * f * Vt / Vs

- for departing

Doppler shift

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