JEE Advanced 2009 Physics question

A student performed the experiment to measure the speed of sound in air using resonance air-column method. Two resonances in the 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,

(A)the intensity of the sound heard at the first resonance was more than that at the second resonanceCorrect
(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 1 cm
(D)the length of the air-column at the first resonance was somewhat shorter than 1/4th of the wavelength of the sound in airCorrect

Answer: (A),(D)

Solution

(A) At the first resonance the vibrating air column is shorter, so less energy is lost and the sound heard is louder: true. (B) The prongs are held in a vertical plane so that they vibrate along the tube's axis: false. (C)

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Question ID VK-037774