tbr doppler effect question

[cloak25]

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If a moving source simultaneously emits two different waves with different frequencies in the direction of motion, what will be observed?

A. only the higher frequency will be doppler shifted
B. only the lower frequency will be doppler shifted
C. the lower frequency signal will experience a greater magnitude of shift
D. the beat frequency will increase in magnitude

answer: D

Explanation says that because both frequencies increase by the same relative amount, the difference between the two values increases, thus the beat frequency must increase. If both frequencies increase by the same amount, then wouldn't the difference between the two remain unchanged? how does beat frequency increase in magnitude?

 

[MedPR]

I don't remember the exact doppler equation, but I know that the frequencies will not increase linearly. In other words, even though they both increase, they will increase by the same factor (say 5) so if the initial frequencies were 5 and 10, they are now doppler shifted to 25 and 50. 10-5 = 5. 50-25 = 25. Beat frequency has increased from 5 to 25.

 

[411309]

Ballin. I got this one right; had to think about it for a few minutes though. Because both frequencies are being admitted in a direction moving toward the source, the perceived frequency for both is getting higher. Say we start out with one frequency at 10 hz, one at 5; the beat frequency is 5. Say the perceived is double due to doppler so now we have 20 and 10 hz. The beat frequency is also doubles and becomes 10. Keep in mind the source is moving closer to the observier so the perceived frequency is higher for both

 

[gettheleadout]

I narrowed this down to C and D and wasn't sure; if I had caught that "magnitude" is the key word here it would have been easy, even without understanding anything about beat frequency.

A and B are wrong because the movement of the source is the same with respect to each of the frequencies emitted. I incorrectly took C to imply that the proportion of the frequency change relative to the emitted frequency is greater in the lower frequency wave (which I think would be true) but this is not what the answer is stating. "Magnitude" refers to the actual change in frequency, which will be the same for each wave. Therefore, C cannot be correct, so the answer is D by POE.

 

[pfaction]

Are these representative of actual questions MCAT may ask?

 

[MedPR]

Are these representative of actual questions MCAT may ask?

Imo, yes.

 

[pfaction]

Wow. This was nothing like AAMC10, which was really easy in the PS...now I'm ****ting my pants for AAMC3...oh god.

 

[Temperature101]

Are these representative of actual questions MCAT may ask?

Unfortunately, yes and even tougher wishy-washy questions.

 

[pfaction]

Oh lord, I have to start ramping my studying up, which I thought I already was. I took it easy today, no more! Tomorrow I hit it HARD

 

[MrNeuro]

I narrowed this down to C and D and wasn't sure; if I had caught that "magnitude" is the key word here it would have been easy, even without understanding anything about beat frequency.

A and B are wrong because the movement of the source is the same with respect to each of the frequencies emitted. I incorrectly took C to imply that the proportion of the frequency change relative to the emitted frequency is greater in the lower frequency wave (which I think would be true) but this is not what the answer is stating. "Magnitude" refers to the actual change in frequency, which will be the same for each wave. Therefore, C cannot be correct, so the answer is D by POE.

Gahhhhh I chose c as well stupid MAGNITUDE

 

[411309]

actually a lot of the questions in this forum are way overblown and detailed and have zero chance of getting asked. This question? Id say a possibility. Most in this forum? prob not, lol.