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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
Hi....I'm not sure why this popped into my head earlier, but it did. If you have a performer running around the stage with an FM transmitter, why doesn't the Doppler effect cause problems?
From my basic understanding of FM radio, this should be causing DC offset by moving the "base line" frequency above or below the carrier frequency the receiver is tuned to. Is it the case that this DOES happen but it's filtered out in the receiver?
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
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Dopler Effect says sound perception changes with distance. If you stay at your distance, you hear true pitch but if move you move toward source, you hear louder pitch and if you move back then you hear softer pitch.

So people on the west train, since they aren't moving from the sound, will hear true pitch whereas people on eastbound train are reducing distance between them and the source of the sound, so will hear an increasing sound.
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
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ArneyViel wrote:
Hi....I'm not sure why this popped into my head earlier, but it did. If you have a performer running around the stage with an FM transmitter, why doesn't the Doppler effect cause problems?
From my basic understanding of FM radio, this should be causing DC offset by moving the "base line" frequency above or below the carrier frequency the receiver is tuned to. Is it the case that this DOES happen but it's filtered out in the receiver?


My two cents would be avoid bringing 'worldly' knowledge to the question. Read the question for what it's worth and don't expand or reduce the scope of the argument.

By this we should just understand Doppler effect as pitch increasing when moving to the source, pitch reducing when moving away from the source and hearing true pitch when not moving.

The trick with this question is to realise that train passengers on Westbound train are not moving 'from the source'.
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
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While we may know about the "Doppler effect" from our high school, the key to answering such questions is to focus on the verbal issues and NOT bring in your own knowledge when answering the questions.
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
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The “Doppler effect” refers to the universally perceived change in the apparent pitch of a sound when that sound is approaching or receding from the listener. Specifically, whenever the distance between the listener and the source of the sound is decreasing, the sound will be perceived by the listener as higher than its true pitch; whenever that distance is increasing, the sound will be perceived by the listener as lower than its true pitch. If the distance between the listener and the source is not changing, the listener will perceive the true pitch of the sound.

Inferences:
If two objects are coming close to each other, then the sound will increase.
If they are moving away, their sound will decrease.
If they stay stationary, the sound pitch will be stationary
Westward travelling train is stationary and eastward-travelling is approaching westward-train

If the above principle holds, which of the following should be observed as an eastward-traveling train is approached by a westward-traveling train that is blowing its horn?

(A) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound lower than the true pitch.
Wrong. It's the opposite. Westward travelling train should hear the original sound as it is stationary.

(B) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound lower than the true pitch.
Wrong. First part is right, but the eastbound train will hear increased pitch as it is approaching the westbound train.

(C) Passengers in the eastbound train should hear the true pitch of the horn; passengers in the westbound train will hear a sound higher than the true pitch.

Wrong. The voice pitch for eastbound trains will increase or decrease as it is not stationary.

(D) Passengers in the westbound train should hear the true pitch of the horn; passengers in the eastbound train will hear a sound higher than the true pitch.
Right. Westbound is stationary and hence will hear the original pitch. Eastbound is approaching westbound and hence the voice pitch will increase.

(E) Passengers in both trains should hear a sound that is higher than the true pitch.
Wrong. One is stationary and one is moving.
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Re: The “Doppler effect” refers to the universally perceived cha [#permalink]
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