# Logs and Decibels Flashcards

1
Q

log 100 = ?

A

2

2
Q

What exactly is a log?

A

An exponent value

3
Q

log 1,000 = ?

A

3

4
Q

log 10,000 = ?

A

4

5
Q

lob 1/ 100 = ?

A

-2

6
Q

log 100,000,000 = ?

A

8

7
Q

lob 1 / 1000 = ?

A

-3

8
Q

log 1 = ?

A

0

9
Q

log 2 = ?

A

0.3

10
Q

log 4 = ?

A

log 4 = log 2 + log 2
= 0.3 + 0.3
= 0.6

11
Q

log 20 = ?

A

log (2 x 10)
= log 2 + log 10
= 0.3 + 1 = 1.3

12
Q

log 400 + ?

A

log (4 x 100)
= log 4 + log 100
= 0.6 + 2
= 2.6

13
Q

What does a dB measure?

A

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

14
Q

State the dB formula for Intensity.

A

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

15
Q

State the dB formula for Amplitude.,

A

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

16
Q

Log 1 / n = ?

A
• log n
17
Q

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

A

dB = 10 log (100/ 1)
= 10 log 100
= 10 (2)
= 20

18
Q

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

A

dB = 10 (-log 1000)
= 10 (-3)
= -30

19
Q

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

A

3 dB

20
Q

Log of (1/2) = ?

A

-0.3

21
Q

What is the wavelength of 7MHz through soft tissue?

A

Soft Tissue = 1.54 mm/µs

(1.54 mm/ µs) / 7 MHz = 0.22 mm

22
Q

Define Attenuate

A

The weakening of sound waves as they travel in the body

23
Q

What is the term meaning a strengthening of ultrasound?

A

Amplified

24
Q

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

A

The Richter scale

25
Q

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

A

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

26
Q

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

A

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

27
Q

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

A

Double

28
Q

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

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