An organ pipe is in resonance with a tuning fork. What change will have to be made in the length l to maintain resonance if
(i) temperature increases
(ii) air is replaced by hydrogen
(iii) pressure is made higher ?

Explanation

If organ pipe is open, its fundamental frequency is `v=(upsilon)/(2l)=(1)/(2l)sqrt((lambdaP)/(rho))`
(i) If temperature increase , `upsilon` increases. To keep v constant, l must be incresed.
(ii) When air is replaced by hydrogen, `rho` decreases. To keep v constant, l must be increased.
(iii) When pressure is made higher, `rho` increases and `P//rho` remains constant. Therefore, no change is required in resonance length.