A line source emits a cylindrical expanding wave. Assuming the medium absorbs no energy find how the ampitude and intensity of wave depend on the distance from the source?

Answer

A

Explanation

Suppose power of linre source is P. Then, at distance r, surface area is `2pirl`.
`:. l = (P)/(S) =(P)/(2pirl)`
or `I prop (l)/( r )`
Further, `I prop A^(2)`
`:. A prop (1)/(sqrt(r))`