Q.
For a person with normal hearing the faintest sound that can be heard at a frequency of 400Hz has a pressure amplitude of about 6×10−5 N/m2. Calculate the corresponding intensity in W/m2. Take speed of sound in air as 344m/s and density of air 1.2 kg/m3
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a
4.4×10−3 W/m2
b
4.4×10−12 W/m2
c
4.4×10−4 W/m2
d
4.4×10−1 W/m2
answer is B.
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Detailed Solution
GivenFrequency f=400 HzPressure ΔP=6.0×10−5 paSpeed of sound in air V=344 m/sDensity of air ρ=1.2 kg/m3Intensity I=vΔP2max2BSubstituting B=ρv2 the above equation reduces to I=(ΔP)max22ρv=6.0×10−522×1.2×344=0.0436×10−10≃4.4×10−12W/m2
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