What do you understand by 'resonance '? How would you use resonanceto determine the velocity of sound in air ?

Explanation

Resonance `:` If the natural frequency of a vibrating body is equal to the frequency of external periodic force then the two bodies are said to be in resonance.At resonance the bodies will vibrate with increasing amplitude.
Determination of velocity of sound in air using resonance `:`
(1) In resonance tube, an air column in made to vibrate by means of vibrating fork. At certain length of air column, the air column would have the same frequency as that of the fork . Then the air column vibrates with the maximum amplitude and the intense sound is produced.
(2) The vibrating fork of known frequency (v) is placed the open end of the tube.
ltbr. (3) The length of air column is gradually increased until the booming sound can be heard at two different lengths of air column.
(4) In first resonance , `l_(1)` be the length of air column, then `( lambda)/(4) = l_(1) + C ` ...(1)
Where `lambda ` is the wavelength of sound emitted by the fork and C is the end correction of the tube.
(5) In second resonance, `l_(2)` be the length of air column, then `( 3lambda)/( 4) = l_(2) + C ` ..(2)
`(2) - (1) implies (lambda ) /( 2) = l_(2)- l_(1)`
`lambda = 2(l_(2)-l_(1))`
Speed of sound is given by
`upsilon = vlambda = v[2( l_(2)- l_(1))]`
`:. upsilon=2v( l_(2)- l_(1))`
(6) Hence by knowing `v,l_(1) ,l_(2)` the speed of sound is calculated.