• # question_answer 45) In a certain organ pipe three successive resonance frequencies are observed at 425,595 and 765 Hz respectively. If the speed of sound in air is 340 m/s, the length of the pipe is: A) 2 m                             B) 1 m                 C)      1.5 m               D)     2.5 m

Successive frequency are in the ratio 425:595:765 i.e., 5:7:9. This indicates that only odd harmonics are present. Hence it is a closed organ pipe. In a closed Organ pipe the frequency of the 5th harmonic is 5v/4 fi where v is the velocity of sound. So,$\frac{5v}{4\ell }=425$where $v=340\,m/s.$ $\therefore$$\ell =1\,m.$ Hence, the correction option is (b).