Frequency or wavelength varies with medium?

[circulus vitios]

TBR Physics Chapter VI, Passage III, Question 15

When a wave travels from air into water, its speed increases by a factor of four. Compared to the wave in air, the transmitted wave has:

A. the same frequency, longer wavelength
B. the same frequency, shorter wavelength
C. the same wavelength, higher frequency
D. the same wavelength, lower frequency

Part of the answer key says

When any wave travels from one medium into another, its frequency remains the same. The only case where the frequency of the wave changes is when the sender or receiver are moving relative to one another.

Passage VI, Question 39 says

(Talking about an open pipe, fn=nv/2L)

To most effectively increase the frequency in the pipe, one should replace the N2 in the air with:

A. He, and lengthen the pipe
B. H2, and lengthen the pipe
C. He, and shorten the pipe
D. H2, and shorten the pipe

Part of the answer key says

Changing the type of air could change the speed of sound... Since a higher speed of sound means a higher frequency...

Uhh, I thought changing the medium couldn't change the frequency?

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[Temperature101]

Electromagnetic wave =|= sound wave. I think the first one is an electromagnetic wave and the second one is a sound wave.

 

[milski]

Once a wave is created, its frequency will state constant.

In the case of the pipe, changing the speed of the sound will change the resonant frequency for the pipe and create a wave with this frequency. Once created, its frequency will stay constant.

The frequency does stay the same for all kinds of waves, does not matter if they're sound, EM or anything else.

 

[Temperature101]

Once a wave is created, its frequency will state constant.

In the case of the pipe, changing the speed of the sound will change the resonant frequency for the pipe and create a wave with this frequency. Once created, its frequency will stay constant.

The frequency does stay the same for all kinds of waves, does not matter if they're sound, EM or anything else.

Thanks...

 

[circulus vitios]

Once a wave is created, its frequency will state constant.

In the case of the pipe, changing the speed of the sound will change the resonant frequency for the pipe and create a wave with this frequency. Once created, its frequency will stay constant.

The frequency does stay the same for all kinds of waves, does not matter if they're sound, EM or anything else.

Thanks.

 

[MedGrl@2022]

TBR Physics Chapter VI, Passage III, Question 15



Part of the answer key says



Passage VI, Question 39 says



Part of the answer key says



Uhh, I thought changing the medium couldn't change the frequency?

What was the answer to the gas question? A heavier, more dense gas right (since the speed of sound increases with mediums that have a greater bulk modulus)? Also doesn't the speed of EM decrease with mediums with higher index of refractions? Why does the question say that it "increases by a factor of four"? This makes no sense to me.

 

[circulus vitios]

What was the answer to the gas question? A heavier, more dense gas right (since the speed of sound increases with mediums that have a greater bulk modulus)? Also doesn't the speed of EM decrease with mediums with higher index of refractions? Why does the question say that it "increases by a factor of four"? This makes no sense to me.

The second question? The answer was D. I used my physical intuition to pick the gas. Your voice shifts to a higher pitch if you huff He (4 g/mol) from a party balloon, so the effects of a lighter gas (diatomic, 2 g/mol) must be even greater.