log 100 = ?

2

What exactly is a log?

An exponent value

log 1,000 = ?

3

log 10,000 = ?

4

lob 1/ 100 = ?

-2

log 100,000,000 = ?

8

lob 1 / 1000 = ?

-3

log 1 = ?

0

log 2 = ?

0.3

log 4 = ?

log 4 = log 2 + log 2

= 0.3 + 0.3

= 0.6

log 20 = ?

log (2 x 10)

= log 2 + log 10

= 0.3 + 1 = 1.3

log 400 + ?

log (4 x 100)

= log 4 + log 100

= 0.6 + 2

= 2.6

What does a dB measure?

the change from initial strength to final strength for Amplitude, Intensity, and Power

State the dB formula for Intensity.

dB = 10 x log ( Final Intensity / Initial Intensity )

State the dB formula for Amplitude.,

dB = 20 x log ( Final Amplitude / Initial Amplitude )

Log 1 / n = ?

- log n

If the Intensity increases by 100, how many decibels has it increased?

dB = 10 log (100/ 1)

= 10 log 100

= 10 (2)

= 20

In the Intensity decreases by 1,000, how many decibels has it decreased?

dB = 10 (-log 1000)

= 10 (-3)

= -30

How many decibels has the Intensity increased if the Intensity has doubled?

3 dB

Log of (1/2) = ?

-0.3

What is the wavelength of 7MHz through soft tissue?

Soft Tissue = 1.54 mm/µs

(1.54 mm/ µs) / 7 MHz = 0.22 mm

Define Attenuate

The weakening of sound waves as they travel in the body

What is the term meaning a strengthening of ultrasound?

Amplified

What is an “everyday” example of a logarithmic scale?

The Richter scale

T/F. A decibel value can by calculated using a single intensity.

False! Two Intensities are required. Decibels measure the ratio of change.

If there is an intensity change from 100 to 10, what is the change in dB?

dB = 10 log ( 1/ 10 ) = -10

In there is an increase of 3 dB, the intensity will _________?

Double

There is an initial intensity of 2 Beebe’s. What is the final intensity if the change is + 9 dB?

3 dB = doubling of intensity 2 doubled = 4 4 doubled = 8 8 doubled = 16 16 Beebe's = Final intensity