In: Physics
The concept used to solve this problem is fundamental frequency.
Use equation of fundamental frequency to find the fundamental frequencies of the standing wave in the test tube.
The expression for the wavelength of the fundamental harmonic for a tube with one end open and other end closed is as follows:

Here,
is the wavelength and
is the length of the tube.
Wavelength is also expressed as

Here,
is the speed of the wave and
is the fundamental frequency.
(a)
The fundamental frequency of the standing wave is,

Wavelength of the fundamental harmonic for a test tube is,

Substitute
as
and
as
.

(b)
The fundamental frequency of the standing wave is,

Wavelength of the fundamental harmonic for a test tube is,

Since the test tube is half filled with water, length
is equal to,
Substitute
as
and
as 

Thus, the frequency of the standing wave is 
Thus, the frequency of the standing wave is 