Logs and Decibels Flashcards
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
