One end of 85 cm long pipe is made closed. Now, normal modes of vibration are set up in the air column, inside this pipe. Find no. of harmonics having frequency less than 1250 Hz. (Velocity of sound in air is 340 m/s.)

One end of 85 cm long pipe is made closed. Now, normal modes of vibrat

1.	One end of 85 cm long pipe is made closed. Now, normal modes of vibration are set up in the air column, inside this pipe. Find no. of harmonics having frequency less than 1250 Hz. (Velocity of sound in air is 340 m/s.)
Answer» 6 4 12 8 Solution :Here `f _(1) = (v)/(4L) = (340)/(4 XX 0.85) =100 Hz` Now, possible vibratons are `f _(1), 3f_(1) , 5f _(1), 7f_(1) , 9f_(1) and 11 f _(1)` with frequencies `100,300, 500,700,900,1100Hz.(because` Here we require `f lt 1250 Hz)` No. of possible harmonics = 6