Question

Which harmonic frequencies can be detected in a tube closed at one end whose fundamental frequency is 200 Hz?

200 Hz

300 Hz

400 hz

600 Hz

1000 Hz

It's a select multiple and I said the last three which was wrong.

Answer 1

You were guessing. wavelength has to be a <b>odd</b> multiple of 200. If you dont get that, there are two of them

Answer 2

node at closed end, max at the open end.
Draw the picture.
first boom at 1/4 of wavelength = length of tube L
say the speed of sound is c

c = wavelength /period = wavelength* f

now we are told that 1/4 wavelength is L
c = 4 L*200 = 800 L
so the next time we have a node at the closed and a max at the open end is when
wavelength = (4/3)L
c = (4/3)L*f = 800 L
f = 800 *3/4 = 600 Hz <-------
the next time is when
5/4 wavelength = L
c = (4/5)L*f= 800 L
f = 1000 Hz <--------
200, 600, 1000