Two sources of sound placed closed to each other, are emitting progressive waves given by
`y_(1)=4 sin 600 pi t`
and `y_(2)=5 sin 608 pi t`
An observer located near these two sources of sound will hear

Options

A. `8` beats per second with itensity ratio `25 : 16` between waxing and waning
B. `8` beats per second with itensity ratio `81 : 1` between waxing and waning
C. `4` beats per second with itensity ratio `81 : 1` between waxing and waning
D. `4` beats per second with itensity ratio `25 : 16` between waxing and waning

Answer

C

Explanation

`(I_(max))/(I_(min))=((A_(1)+A_(2))^(2))/((A_(1)-A_(2))^(2))=((5+4)^(2))/((5-4)^(2))=(81)/(1)`
`2piv_(1)=600pi` so `v_(1)=300Hz`
`2piv_(2)=608pi` so `v_(2)=304Hz`
No. of beats per sec `v_(2)-v_(1)=4`