Destructive interference in a speaker value

AI Thread Summary
The discussion revolves around calculating the position for complete destructive interference of sound waves emitted from two speakers. The speakers are located at (0, 0) and (0, 4.00) meters, emitting waves of wavelength 1.55 m. The path difference formula is used to find the smallest positive x on the x-axis where interference occurs, initially leading to incorrect calculations. A critical realization is that using a path difference of 2.5 (n=2) yields the correct smallest value of x, which is 0.127 meters. The error stemmed from misinterpreting the path difference requirement for destructive interference.
jwbehm
Messages
12
Reaction score
0

Homework Statement



Speaker 1 is positioned at the origin and speaker 2 is at the position (0, 4.00) meters. They emit identical sound waves of wavelength 1.55 m, in phase. If you stand on the x-axis at (x, 0) meters, what is the smallest positive value for x for which you experience complete destructive interference?

Homework Equations



A^2+ B^2 = C^2
P2-P1= (n+.5)λ
V= λf

The Attempt at a Solution



My main question, though its possibly not where I am going wrong, is would n have to equal 0 for it to be lowest destructive interference?
 
Physics news on Phys.org
Excuse my poor handwriting. . .
scan0002-1.jpg


After plugging in all variables I came up with 9.94, which is incorrect. Is N supposed to equal 0 for this problem?

p1 is from the bottom speaker to the listener and p2 is the hypotenuse
 
The work you did seems to be on the right track, but perhaps use of different notation will clear things up. Since one speaker is located at the origin (0, 0) and the other speaker is located at (0, 4), we do not need the co-ordinates of the Point P1-P2 but rather its distance:

Since the Path Difference/ Wavelength = 0.5 (you had written n+0.5 but since we are looking for the smallest value, 0.5 will work), we can express the path difference as:
x units from the speaker at the origin
Sqrt(x^2 + 4^2) units from the speaker at (0, 4)

Thus: Path difference = Sqrt(x^2 + 4^2) - x
Wavelength = 1.55

The rest is for you to solve.
 
Hmm that gives me the answer I had already come up with which was incorrect, 9.935. Let me make sure I'm following you right

Path difference = Sqrt(x^2 + 4^2) - x

Here I'm plugging in wavelength/2, thus

.775 = Sqrt(x^2 + 4^2) - x
which brings me to
(x+.775)^2= x^2+ 4^2
which eventually goes to
1.55x-15.4=0
Thus x= 9.935. . . which is incorrect.
 
Ahh. I see my mistake. My mistake was assuming that the Path Difference/ Wavelength = 0.5. A value of 0.5 for the P.D./wavelength is not the smallest path difference. From a bit of trial and error, you will see that 2.5 (i.e. n=2, n+0.5 = 2,5) creates the smallest path difference with an answer of x=0.127.

I am sorry I have made such a basic error.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
Back
Top