Logs and Decibels

Question 1

log 100 = ?

Answer 1

2

Question 2

What exactly is a log?

Answer 2

An exponent value

Question 3

log 1,000 = ?

Answer 3

3

Question 4

log 10,000 = ?

Answer 4

4

Question 5

lob 1/ 100 = ?

Answer 5

-2

Question 6

log 100,000,000 = ?

Answer 6

8

Question 7

lob 1 / 1000 = ?

Answer 7

-3

Question 8

log 1 = ?

Answer 8

0

Question 9

log 2 = ?

Answer 9

0.3

Question 10

log 4 = ?

Answer 10

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

Question 11

log 20 = ?

Answer 11

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

Question 12

log 400 + ?

Answer 12

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

Question 13

What does a dB measure?

Answer 13

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

Question 14

State the dB formula for Intensity.

Answer 14

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

Question 15

State the dB formula for Amplitude.,

Answer 15

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

Question 16

Log 1 / n = ?

Answer 16

• log n

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

3 dB

Question 20

Log of (1/2) = ?

Answer 20

-0.3

Question 21

What is the wavelength of 7MHz through soft tissue?

Answer 21

Soft Tissue = 1.54 mm/µs

(1.54 mm/ µs) / 7 MHz = 0.22 mm

Question 22

Define Attenuate

Answer 22

The weakening of sound waves as they travel in the body

Question 23

What is the term meaning a strengthening of ultrasound?

Answer 23

Amplified

Question 24

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

Answer 24

The Richter scale

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

Double

Question 28

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

Answer 28

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