Chapter 14 - Sound - Learning Path Questions and Exercises - Exercises - Page 524: 22

a). $1.25\times10^{-15}W$ b). $1.25\times10^{-3}W$

a). Threshold of hearing = $10^{-12}W/m^{2}$ $P=I.A=10^{-12}\times 4\times pi \times(\frac{1}{100})^{2}=1.25\times10^{-15}W$ b). Threshold of pain = $1W/m^{2}$ $P=I.A=1\times4\times pi \times(\frac{1}{100})^{2}=1.25\times10^{-3}W$