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More Than 475 Free MCAT Questions with Detailed Answers!

Physics - Sound Waves

When we talk about sound waves, we usually mean sound waves we can hear. The human ear can detect sounds in the frequency range of 20 hertz to 20,000 hertz. That is the same as saying 20 cycles per second to 20,000 cycles per second.

Another name for frequency is pitch. When sound pitch is above the audible range, it is called ultrasonic. When sound pitch is below the audible range, it is called infrasonic.

Loudness

When we’re talking about sound and we say loud, we are talking about two closely related quantities; intensity and loudness.

Intensity is measured in watts per square meter or W/m2. Loudness is measured in decibels, dB.

Here is the equation that relates loudness to intensity.

Rule number 40:
Loudness in decibels equals ten times the log of the intensity over the intensity at the threshold of hearing. The threshold of hearing is 10-12 watts per m2. This is what the formula is really saying.

If we multiply any given intensity by 10, we add 10 decibels to the associated loudness per intensity level. But if we multiply any given intensity by 100, we add 20 decibels to the associated loudness per intensity level. And if we multiply any given intensity by 1000, we add 30 decibels to the associated loudness per intensity level.