i also know that intensity of waves = P/2∏r (for circular waves) , where power = 0.5m(w^2)(A^2)s^-1 , after substituiting the P inside , i have I = 0.5m(w^2)(A^2)s^-1 /2 pi r.

the amplitude is a or a/x ?

so i can say that I is directly proportional to (A^2)/r .
but in the question, the solution gives I is directly proportional to (A^2) but not I is directly proportional to (A^2)/r .

Taking I is directly proportional to (A^2)/r ,
provided a (amplitude ) is constant, so i have I is directly proportional to 1/x as in the working.
[IMG]http://i.imgur.com/dyt0gKc.jpg[/IMG]

Question

i also know that intensity of waves = P/2∏r (for circular waves) , where power = 0.5m(w^2)(A^2)s^-1 , after substituiting the P inside , i have I = 0.5m(w^2)(A^2)s^-1 /2 pi r.

the amplitude is a or a/x ?

so i can say that I is directly proportional to (A^2)/r . 
but in the question, the solution gives I is directly proportional to (A^2) but not I is directly proportional to (A^2)/r . 

Taking I is directly proportional to (A^2)/r , 
provided a (amplitude ) is constant, so i have I is directly proportional to 1/x as in the working. 
[IMG]http://i.imgur.com/dyt0gKc.jpg[/IMG]

anonymous · Answer

[IMG] http://i.imgur.com/EjrGT4k.jpg [/IMG] (actiual ans) [IMG] http://i.imgur.com/Qrycnlm.jpg [/IMG] (hand written working)

anonymous · Answer

it doesn't say it's circular wave so you use the wrong equation
it say the wave go along x-axis so power=Intensity here