(i) What is beat phenomenon?
(ii) A whistle revolves in a circle with angular velocity of `omega=20rads^(-1)`. If the frequency of sound is 385 Hz and speed is 340 `ms^(-1)`, then find the frequency heard by the observer when the whistle is at B.

Explanation

(i) When two sound waves of different frequency approach your ears, the alternating constructive and destructive interference cause the sound to be alternatively soft and loud this phenomenon which is called ‘beating’ or producing beat occurs. The beat frequency is equal to the absolute value of the difference in frequency of the two waves
(ii) Speed of source (whistle), `v_(S)=romega=0.5xx20=10m//s`
Actual frequencyy=v=385Hz
Sped of sound, v=340m/s
When the whistle (at point B) is moving towards the observer, then frequency
`v'=(v)/(v-v_(S))xxv=(340)/(340-10)xx385=396.7Hz`.