Computing

82 ◾ Computing

At present, logarithms are used in the denitions of various forms of

measurement. For example, the scale of an earthquake is measured by its

magnitude M, dened as

log

10

E = 4.8 + 1.5M,

where E is the energy (Joule) of the earthquake wave.

Another example is the measure for acidity and basicity of an aqueous

solution known as pH in chemistry, dened as

pH = –log

10

a

H

+

,

where a

H

+

is the hydrogen ion activity.

e decibel (denoted by dB) is also a logarithmic unit, commonly

used in physics and engineering to express the ratio between two values.

Forexample, the gain of a voltage amplier that amplies v

i

volts to v

o

volts

is ...