PHYS 1070 Lecture Notes - Lecture 5: Sound Energy, Wave, Inverse-Square Law
25 Mar 2015
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Phys1070: intro physics for life sci - lecture 5: energy, power and intensity. Sound is a disturbance in a medium. Energy is needed to create this disturbance (units = joules) When you create sound, you use up energy which the wave can then carry away in the form of vibrating molecules. Assuming sound lasts for some time t" we can introduce 2 new terms : Intensity is a property which explains loudness. Assume sound radiates equally in all directions. Assume sound energy is not absorbed (conservation of energy) The total power (and energy) is evenly distributed over the surface of this sphere. As r increases, i decreases = inverse square law . Energy is conserved, therefore power is additive. Intensity is inversely proportional to the distance squared. Q: an instructor slams a stick on the desk that lasts 0. 1s and has a power of 0. 5mw. A: p=e/t e=p(t) = 5x10-4 (0. 1) = 5x10-5 joules.
