Reflection of sound wave in an open organ pipe

[vcsharp2003]

Homework Statement

How and why does a sound wave get reflected from the open end of an organ pipe?

Relevant Equations

None

I know that standing waves form in an open organ pipe. Since, standing waves can only form from superposition of original wave and reflected wave, so there must be a reflected wave in an open organ pipe. But I fail to understand how sound wave can reflect at the open end of organ pipe.

 

[Orodruin]

Why does this surprise you? It will be easier to address your question if you give the reasoning.

 

[vcsharp2003]

Why does this surprise you? It will be easier to address your question if you give the reasoning.

My understanding is that the sound wave should travel through the open end since there is no barrier. The air particles in a sound wave are vibrating parallel to wave direction. At the open end, the air particles vibrating should cause the air particles just outside the pipe to also start oscillating resulting in a wave outside the tube. The open end cannot exert a force on the air particles just inside the pipe to cause a reflected wave unlike a closed end.

 

[Orodruin]

Consider this: At the open end, pressure is approximately constant. If there was just a wave towards the open end, there is no way that pressure could be maintained constant.

 

[vcsharp2003]

Consider this: At the open end, pressure is approximately constant. If there was just a wave towards the open end, there is no way that pressure could be maintained constant.

So, when pressure is low just inside the open end then air from outside would rush to inside the open end causing particles to move just inside the open end resulting in a wave traveling in opposite direction to original wave.

If pressure is high just inside the tube compared to outside then air would rush towards the outside that causes air particles to move just inside the open end resulting in a new wave/ disturbance inside the pipe in opposite direction to original wave.