Waves (EDITED)

thanks to km for asking mi some old old physics qtn... then i realised there are 2 impt formulae tt are perhaps taught last time.. but not now(which means out fo syllabus)... but seems like quite useful.. ahah anyway i derive e formulae from e qtns.. so might not be fully accurate =/ but so far work wonders.. anyway duno we did learn or not lahz.. haven study waves yet.. but km say nvr see e formulae b4

for same frequency(i think)..
a' = (s/s')a
where a' is new amplitude, a is old amplitude, and s' is new distance from source and s is old distance from source

the other one derived frmo this formula..links intensity to distance from source..
(I'/I)^½ = s'/s
i.e ... root of (I' which is new intensity over I which is old intensity) = s'/s which is new distance from source over old distance from source

so far these 2 formulae i only used on qtn tt only includes 1source.. means if 2 sources duno can work or not... most prob cant? anyway e qtns tt i used wif these formulae are from page 152, qtn 10,page 154, qtn 25,26 .... although concept might be wrong or duno wad.. but duno y can work =/

zhongwei

EDIT: a fren of mine got 1 more input ... I = P/[4r²(pi)] .. intensity = power over surface area of sphere... since when source in middle... the waves will travel all around 360° thus is sphere..
"--- says: yes..so it tells tt the intensity..hmm...of the sound from an pt source decreases with the square of the distance r from the source"
which goes to show... as disatnce increases... intensity decreases.. and this means amplitude decreases as well... hmm?