A tuning fork vibrates with frequency 256 Hz and gives one beat per second with the third normal mode of vibration of an open pipe. What is the length of the pipe? (speed of sound in air is 340 m s - 1 )

Question

A tuning fork vibrates with frequency 256 Hz and gives one beat per second with the third normal mode of vibration of an open pipe. What is the length of the pipe? (speed of sound in air is 340 m s - 1 ), 220 cm, 200 cm, 190 cm, 180 cm

MARKS App · Accepted Answer

Organ pipe will have frequency either 255 or 257 Hz . Using 255 Hz , 255 = 3 v 2 l , ⇒ l = 3 × 340 2 × 255 m ⇒ l = 200 cm . Using 257 Hz , 257 = 3 v 2 l ' ⇒ l ' = 3 × 340 2 × 257 m = 198 cm .

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