"Pipe A has length L and is open at one end and closed at the other. Pipe B is open at both ends and has length 2L. Which harmonic of pipe B matches in frequency the fundamental of pipe A?"

Explanation:

length of pipe A is L

frequency of fundamental note of pipe A which is closed organ pipe

= velocity of sound / 4 x length of pipe

=  V / 4 x L where V is velocity of sound .

Similarly frequency of fundamental note of pipe B which is open organ pipe

= velocity of sound / 2 x length of pipe

= V / (2 x 2L) =  V / 4L , This is also called first harmonic

so fundamental frequency of pipe A will be equal to first harmonic of pipe B .

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.