Is there any difference in a wave if its in dry air or moist air? Please help me out.

[graphicer89]

Homework Statement

A) A tuning fork is struck in dry air. Then it is struck in moist air. Under whch conditions do the sound waves from the tuning fork move more quickly?

B) No matter what the temperature if the air, the frequency produced by a tuning fork remains the same. Would the wave length produced by the tuning fork be longer in dry air
or moist air? Why?...

Homework Equations

None i guess...

The Attempt at a Solution

A) My guess is that it would move faster in dry air.

B) I would say that the wavelengths are longer in moist air because the moist air acts like a resistance no? making the waves go slower thus increasing the wavelength...i looked every where and i just can not find anything on this...please help me out...whats the physics here involved?




These are extra questions and i just need help zoning in on the answers...please help me out if you desire...


20) When blue light strikes an opaque object whose resonant frequency is lower than the frequency of blue light what happes?
A) The amplitude of the vibrations of the electrons in the glass becomes larger
B) The object becomes warm
C) The blue light is absorbed without reemission
D) The blue light is reflected by the electrons in the object
E) The blue light is transmitted throught the object

(For 20 i know the answers ARE NOT A,B, and E...leaving C and D...but i don't know which one could fit in the answer...please help me out...)

15) When blue light strikes an opaque object whose resonant frequency is the same as the frequency of the blue light what happens? ( Choose as many as apply)
A) The amplitude of the vibrations of the electrons in the glass becomes larger
B) The object becomes warm
C) The blue light is absorbed without reemission
D) The blue light is reflected by the glass
E) The blue light is transmitted throught the glass

(for 15 i know the answers ARE NOT E...I know the Answer is B and C but what about A and C? Do they apply??

 

[berkeman]

Google speed of sound equation for your first question -- that will get you info on how the speed varies with pressure, humidity, temperature, etc.

 

[graphicer89]

Google speed of sound equation for your first question -- that will get you info on how the speed varies with pressure, humidity, temperature, etc.

Done and done ..did that ...

So for A it would move a little more quickly in moist air...

For B I am looking for the reference but well nothing comes to hand...

 

[berkeman]

Frequency the same, speed is higher, so the wavelength has to be ______

 

[graphicer89]

Frequency the same, speed is higher, so the wavelength has to be ______

Shorter no? I am trying to visualize it...Same frequency but just faster its like a roller coaster going up and down really fast...sorry if i have a limited scope on physics...

 

[berkeman]

To visualize it, think of a sine-wave shape whatever going past you. To hear the same frequency, you need to hear the same number of peaks per second going past you. If the waveform goes faster past you, but you hear the same number of peaks per second, do the peaks have to be closer together or farther apart on the waveform.

To think about it mathematically, look at the units of each quantity, and write the equation based on the units.

Velocity is in [m/s]
Wavelength is in [m]
Frequency is in [Hz] = [1/s]

Now write the equation for the wavelength in terms of velocity and frequency. What happens to wavelength when frequency stays the same, and velocity goes up?

 

[graphicer89]

To visualize it, think of a sine-wave shape whatever going past you. To hear the same frequency, you need to hear the same number of peaks per second going past you. If the waveform goes faster past you, but you hear the same number of peaks per second, do the peaks have to be closer together or farther apart on the waveform.

To think about it mathematically, look at the units of each quantity, and write the equation based on the units.

Velocity is in [m/s]
Wavelength is in [m]
Frequency is in [Hz] = [1/s]

Now write the equation for the wavelength in terms of velocity and frequency. What happens to wavelength when frequency stays the same, and velocity goes up?

Well the peaks have to be closer together to maintain the same frequency...

isnt the equation...velocity = wavelength x frequency...for the frequency= velocity/wavelength...


so i will put an example...

velocity 10 m/s
wavelength 5 m
Frequency 2 hz ...5 x 2 =10 ...2=10/5...if wavelength gets bigger the frequency gets smaller...

 

[berkeman]

Well the peaks have to be closer together to maintain the same frequency...

Not if the speed of the waveform going by is increased...

isnt the equation...velocity = wavelength x frequency...for the frequency= velocity/wavelength...


so i will put an example...

velocity 10 m/s
wavelength 5 m
Frequency 2 hz ...5 x 2 =10 ...2=10/5...if wavelength gets bigger the frequency gets smaller...

The frequency is CONSTANT in this question, right? What happens if you hold frequency constant, and increase velocity? What must happen to the wavelength?

 

[graphicer89]

To visualize it, think of a sine-wave shape whatever going past you. To hear the same frequency, you need to hear the same number of peaks per second going past you. If the waveform goes faster past you, but you hear the same number of peaks per second, do the peaks have to be closer together or farther apart on the waveform.

To think about it mathematically, look at the units of each quantity, and write the equation based on the units.

Velocity is in [m/s]
Wavelength is in [m]
Frequency is in [Hz] = [1/s]

Now write the equation for the wavelength in terms of velocity and frequency. What happens to wavelength when frequency stays the same, and velocity goes up?

Not if the speed of the waveform going by is increased...



The frequency is CONSTANT in this question, right? What happens if you hold frequency constant, and increase velocity? What must happen to the wavelength?

Wow I am trying to think...but just won't come to mind...

2=10/5 ...you have to increase the wavelength no? Make it bigger? so like it would be 20/10 , then 30/15 ...yea you would increase it and make it bigger if I am not mistaken

 

[berkeman]

Wow I am trying to think...but just won't come to mind...

2=10/5 ...you have to increase the wavelength no? Make it bigger? so like it would be 20/10 , then 30/15 ...yea you would increase it and make it bigger if I am not mistaken

Whew, yes. Constant frequency, increasing speed means longer wavelength.

Sorry, I'm no help on your subsequent blue light questions. You might want to post them as a separate thread, since this one has gone on this long just on the first question.

 

[graphicer89]

Whew, yes. Constant frequency, increasing speed means longer wavelength.

Sorry, I'm no help on your subsequent blue light questions. You might want to post them as a separate thread, since this one has gone on this long just on the first question.

Oh man I am extremelly sorry if i have to put you threw all of this...patience is a virtue that a lot of people don't have...im self teaching my self all this so i have to rely on this forum and in this on case on you...but i will try that ...though..thanks so much for your help...