Sound Intensity and Human threshold for hearing

AI Thread Summary
A sound below the threshold of human hearing is often described in terms of negative intensity levels in decibels (dB). The discussion highlights that while sound intensity can be measured in watts per square meter (W/m^2), negative values in this context are not physically meaningful. The confusion arises from the difference between intensity levels in dB and actual intensity values in W/m^2. The consensus leans towards the understanding that sound intensity cannot be negative, as it is a measure of power per area. Clarifying these concepts is essential for accurately interpreting sound intensity and human hearing thresholds.
mssweeteypie
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Is it possible to have a negative sound intensity level?
A sound that is below the threshold of human hearing has...

(A) a negative intensity level (in dB).
(B) a negative intensity (in W/m^2 ).
(C) an intensity level of zero.
(D)an intensity level less than 1 dB , but greater than 0.

I think I know the answer but I don't want to guess wrong and lose points.



Does it have to do with anything like I/Io or I=power/area ??


I think the answers is A or B..but I don't see the difference in between dB and W/m^2 i thought they are the same thing.
 
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I think you're confusing yourself. Look at the units in answers A and B and ask yourself how each could physically be negative.
 
Thread 'Variable mass system : water sprayed into a moving container'

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}...
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