help with sound

[TyErd]

how do i do this question

[m@tty]

So with a standing wave each antinode oscilates up and down in a single period. After a quarter of a period all of the parts which were above are on the line and all the bits which were below are also on the line.

With a standing wave it goes like this, using figure 3 as an example:

Taking t=0 - Figure 3.

Then at t=T/4 its all flat

At t=T/2 its a reflection of figure 3. the high pressure antinodes become low pressure and vice versa.

At t=3T/4 its flat again.

Finally at t=T, after a whole period, its back to figure 3.


So the times you're looking for are T/4 and 3T/4.

[TyErd]

ohh i get it, is the wave always reflected when t= T/2? in every standing wave?

[m@tty]

Yeah, that's right.

A defining factor of a standing wave is that the nodes and antinodes don't shift.

But it still follows the normal wave form(in terms of pressure variation. So easy to forget this.. =S).
So the antinodes have to get back to the same position in a whole wavelength.
Every T/4 the antinodes move from high/low pressure to normal or normal to high/low.

[TyErd]

ohkay thank vm!

[chap]

so whats the answer in time? .075 seconds?
I thought it would just be .2 seconds, 2 periods.

[m@tty]

Haha this is a spring .. didn't even realise xD It's inconsequential though..
The first two answers are 0.025 and 0.075 seconds - T/4 and 3T/4 respectively.

What do you mean by your second answer of ".2 seconds, 2 periods"?

[chap]

oh nevermind I see now...