[PHYS 224] - Final Exam Guide - Comprehensive Notes for the exam (36 pages long!)

• School: McGill University
• Department: Physics
• Course: PHYS 224
• Professor: Andrew Mc Cann

Document Summary

Decibel: used to measure ratio between 2 values; a convention (no real units) Used when the range of values is very large. Can be applied to any system (sound intensity, earthquake richter scale) Decibel formula: (cid:1845)=(cid:883)(cid:882) (cid:1864)(cid:1859)(cid:2869)(cid:2868)[(cid:3049)(cid:3028)(cid:3048)(cid:3032) (cid:2870) (cid:3049)(cid:3028)(cid:3048)(cid:3032) (cid:2869)] (sil stands for sound intensity level) Problem: for db to work, you need 2 values (because it is the ratio between 2 values). Intensity is expressed in w/m2 (e. g. 1 10-12 w/m2) Chosen value for sound is 1 10-12 w/m2 (the bottom of human threshold of hearing) Example: (cid:1845) (cid:4666)(cid:1856)(cid:4667)= (cid:883)(cid:882) (cid:1864)(cid:1859)(cid:2869)(cid:2868)[(cid:883)(cid:882) (cid:2869)(cid:2870) /(cid:1865)(cid:2870) (cid:883)(cid:882) (cid:2869)(cid:2870) /(cid:1865)(cid:2870)]=(cid:883)(cid:882) (cid:1864)(cid:1859)(cid:2869)(cid:2868)(cid:883)=(cid:882) (cid:1856) Remember log rules: loga(xy) = logax + logay, loga (xy) = logax logay, loga(xr) = rlogax, logaa = 1 loga1 = 0, (cid:1855)(cid:3042)(cid:3034)(cid:3028)= I = power/area, usually area is either a sphere"s surface area or a semi-sphere"s surface area. The intensity of a sound is the sum of intensities of sine waves which make up the sound.