# Too quiet to hear human senses hearing seeing touch

This preview shows page 1. Sign up to view the full content.

This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ual. ∂s ∂t ￿2 s = smax cos(kx − ω t + φ) 1 = ρ(Area)vsound ω 2 s2 sin2 (kx − ω t + φ) max 2 1 22 I = ρvsound ω smax 2 Monday, October 14, 2013 1 (sin (∗) = ) 2 2 (For point source, s ~ 1/r) Ipoint source = Ps /4π r2 Intensity & sound level −12 β ≡ (10dB ) log10 (I/10 2 W/m ) I = 10−12 W/m2 → β = 0 “What?” Too quiet to hear. Human senses (hearing, seeing, touch, smell, taste) detect intensities I on a log scale. Which is good! Can detect over a large I range, from faint to huge. Conversation has beta about 60dB. Loud rock concert is about 110dB. Pain threshold is about 120dB. Monday, October 14, 2013 Waves in pipes! p (gauge) =0 at open ends s=0 at closed ends So, the wave eqn. BCs are: s|closed = 0 (Just like with a string at ﬁxed end.) Monday, October 14, 2013 and ∂s p = −B ∂x ∂s |open = 0 ∂x (Just like with a string at a free end.) Pipe wave harmonics (Drawing wave’s s displacement. Pressure is ~ derivative, so opposite.) λ = 4L/nodd One end open, one end closed Monday, October 14, 2013 λ = 2L/n Both open, or both closed s & p in pipes Monday, October 14, 2013 The math for pipe wave y z x x=0 s(t, x = 0) = 0 x=L ∂s (t, x = L) = 0 ∂x s = smax sin(kx) cos(kvt + φ0 ) B.C.@L: cos(kL) = 0 k = 2π /λ Monday, October 14, 2013 1 kL = (n + )π 2 L = (2n + 1)λ/4 Math for other cases Both ends closed: B.C.@L: Both ends open: B.C.@L: Monday, October 14, 2013 s = smax sin(kx) cos(kvt + φ) kL = nπ λ = 2L/n s = smax cos(kx) cos(kvt + φ) kL = nπ λ = 2L/n Interference Superpose two traveling wa...
View Full Document

## This note was uploaded on 02/11/2014 for the course PHYSICS 2C taught by Professor Hicks during the Fall '09 term at UCSD.

Ask a homework question - tutors are online