- #1
tsumi
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Homework Statement
p(t)={ -1 from -1/220 to -1/330
0 from -1/330 to -1/660
1 from -1/660 to 1/660
0 from 1/660 to 1/330;
-1 from 1/330 to 1/220 }
p(t) represents the period of the excess air pressure of a sound wave. Find the harmonics and their intensity.
Homework Equations
(1) p(t) = A0/2 + Ʃ ( An cos(2.n.pi.f0.t) + Bn sin(2.n.pi.f0.t) )
(2) An = 2f0 ∫ p(t).cos(2.n.pi.f0.t) dt (from 0 to 1/f0)
(3) Bn = 2f0 ∫ p(t).sin(2.n.pi.f0.t) dt (from 0 to 1/f0)
The Attempt at a Solution
This problem seams quite simple, but I am going crazy with it.
f0 the fundamental frequency, is the frequency of p(t) which is 110.
If you draw p(t) you can easily verify that it is an even function, so you will only need to calculate the coeficients An, using equation (2). This is so, because the integral of p(t) (even) times sin(2.n.pi.f0.t)(odd) yealds zero.
So I integrate p(t).cos(2.n.pi.f0.t) from zero to 1/220 and multiply by 2 in order to find An, but what I get is An=0, and it just can't be =S
I tried other equivalent approaches like integrating from -1/220 to +1/220; integrating from -1/220 to 0 and multiply by 2; etc. Always 0.
Would somebody help?