June 2005 aqa physics paper question on stationary waves

[bonbon22]

Homework Statement

http://downloads.umutech.net/Physics/Past_Papers/PA04/June%202005/Physics%20U4B%20QP%20June%202005.pdf

https://umutech.net/past_papers.html
to the right june 2005 section B first question if the first link does not work

Relevant Equations

First harmonic equation?

A couple of questions on this. How would the sound get reflected back from the surface of the water? And therefore create a stationary wave would the sound not travel though the water at a faster speed then reflect back and intefere? Or does a small amount of the sound reflect back? Part B mentions a frequency and two different lengths, so could it be possible to get the same frequency at two different haromics?

 

[haruspex]

How would the sound get reflected back from the surface of the water?

Any change in medium causes some reflection. You can see yourself reflected in a pane of glass if you are lit as much as the view on the other side of the glass.

 

[haruspex]

Relevant Equations: First harmonic equation?

Why only the first harmonic?

 

[bonbon22]

Why only the first harmonic?

In my aqa spec their is the first harmonic equation f=1/2l * square root (tension/meu) i relaise that to get the 2nd and third harmonics you have to simply times by the frequency, so i mentioned the first harmonic equation. Not sure where to start on part B however.

 

[haruspex]

to get the 2nd and third harmonics you have to simply times by the frequency

Times the frequency by what, exactly? The airspace is closed at one end and open at the other.

where to start on part B

Since a given length can correspond to multiple frequencies (harmonics) it is also true that a given frequency can correspond to multiple lengths.