LOGARITHMIC SCALES

RICHTER SCALES

Richter Scales define the magnitude of an earthquakes:

I:  Intensity of earthquake
I₀:  Intensity of reference earthquake
M: Magnitude of the earthquake (Richter number)

SOUND LEVELS

I:  Intensity of sound (W/m²)
I₀:  Intensity of sound at the threshold of hearing (I₀ = 10^-12 W/m²)
L:  Loudness of the sound (dB)
1 bel = 10 dB

Threshold of hearing is the minimum intensity detectable by the human ear.  Loudness of sound at the threshold of hearing is equal to zero dB.  Threshold of pain is about 120 dB.

pH SCALES

pH = - log [H⁺]

pH: Acidity liquid (0 to 14)

[H⁺]:  Number of moles of hydrogen ions per litre (mol/L)

pH = 7 for distilled water
pH < 7 for an acidic solution
pH > 7 for a basis solutions (alkaline)