Resonance tube experiment

1. The problem statement, all variables and given/known data
A student performed the experiment to measure the speed of sound in air using resonance air-column method. Two resonances in air column were obtained by lowering the water level. The resonance with the shorter air column is the first resonance and that with the longer air column is the second resonance. Then choose correct options

A) The intensity of sound heard at the first resonance was more than that at the second resonance.
B)the prongs of the tuning fork were kept in a horizontal plane above the resonance tube.
C)the amplitude of vibration of the ends of the prongs is typically around 1cm.
D)the length of the air column at the first resonance was somewhat shorter than 1/4th of the wavelength of the sound in air.

3. The attempt at a solution

If I consider first option, I don’t think it is correct as the intensity will not change. In both cases resonance occurs. So it should be same. option B) is incorrect as it is kept in vertical plane. I have no idea about C). The difference in length of two air columns should be λ/2. But from this I cannot make out about length of first air column.

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