推 ihatemath:能量的話是用10，壓力用20 01/08 01:39
不好意思 第2題是40dB沒錯喔 所以答案是(D)
也就是講義乘以20是沒錯的(在這個單位下)
以下是我找到的資料：
Sound is normally measured by a relative scale called a decibel (DB). A
decibel is defined with the equation 10 log (s2/s1) where the logarithm is to
the base of 10 and s2 and s1 are magnitudes of sound signals. Sound is
usually measured with microphones and they respond (approximately)
proportionally to the sound pressure, p. The power in a sound wave, all else
equal, goes as the square of the pressure. The log of the square of x is 2
log x, which introduces a factor of 2 when we convert to decibels for
pressures. Thus a decibel is defined 20 log (p/po), where p is the pressure
and po is reference value. This reference is an estimate of the typical human
auditory threshold in a young person. This value is assumed to be 0.000204
dyne/cm2 (or 0.02 , in microPascals). (This is very low, about 20 billionths
of an atmosphere.)
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