Heres the situation, You have 2 point sources producing circular water waves, in which the phase is adjustable. The question is In what respects does the interference pattern change and in what respects does it stay constant when the relative phase of your sources changes from 0 degrees to 180 degrees? From my testbook I know that 180 degrees means out of phase... but I still dont know how to answer this question. All I know is that the answer should deal with those nodal lines. Can anyone please help?