The Nature of Sound II

Question 1

trig and the unit circle

Answer 1

If r = 1 then
cos=x and sin=y
so (x,y) = (cos,sin)

Question 2

what are rectangular coordinates on the unit circle?

Answer 2

(1,0)
(0,1)
(-1,0)
(0,-1)

Question 3

what are polar coordinates on the unit circle?

Answer 3

(r,θ)

Question 4

unit circle quadrants and location

Answer 4

I, II, III, IV
I= top right
II- top left
III- bottom left
IV= bottom right

Question 5

Uniform circular motion (UCM)

Answer 5

motion of an object in a circular fashion that travels at a constant speed

Question 6

what is often shown as UCM?

Answer 6

SHM simple harmonic motion

Question 7

Trace Uniform projected motion

Answer 7

t= 1 unit

Question 8

sound is created by

Answer 8

movement of air particles and that movement creates pressure variations above and below atmospheric pressure

Question 9

pressure

Answer 9

reported in Pascals (Pa)

Question 10

atmospheric pressure values

Answer 10

kilopascals (kPa)

Question 11

low level sound pressure values

Answer 11

micropascals (µPa)

Question 12

pressure representations in graphs

Answer 12

• the darker bands overlap with the waveform when it is at its positive peak (more pressure)
• the lighter bands overlap with the waveform when it is at its negative peak (less pressure)

Question 13

what do the simple signals repeating at a specific rate imply?

Answer 13

• there is a specified # of complete cycles occurring in 1 second
• there is a specific # of seconds or µseconds that elapse when 1 cycle is completed

Question 14

Wavelength (λ)

Answer 14

distance between two points in a waveform that are the same in terms of pressure

Question 15

how is wavelength determined?

Answer 15

number of complete cycles in a unit of time and the medium in which the sound pressure variations propagate

Question 16

wavelength equation

Answer 16

λ= c x T or λ= c/f
c= speed of sound (343 m/s) and t= period
T=1/f

Question 17

the higher the amplitude…

Answer 17

the higher the energy present in the waveform

Question 18

5 different ways to describe amplitude

Answer 18

peak amplitude
peak-to-peak amplitude
instantaneous amplitude
RMS amplitude
dB

Question 19

peak amplitude

Answer 19

max deviation from zero

Question 20

peak-to-peak amplitude

Answer 20

change between peak (highest amp) and trough (lowest amp)

Question 21

RMS amplitude

Answer 21

root mean square or average amplitude
PURE TONE= 45 degrees or 0.707 peak

Question 22

phase

Answer 22

• description of the position of a point in time on a waveform
• relative displacement of waves that have the same frequency

Question 23

how many degrees is a complete cycle?

Answer 23

360

Question 24

phase of a sine wave

Answer 24

One complete cycle from 1 to 2
- starting phase is 0 deg
- at the peak the phase is 90 deg
- back at equilibrium the phase is 180 deg
- another quarter cycle the phase is 270 deg
- back at equilibrium is 360 deg or returns to 0

Question 25

out of phase quarter cycle

Answer 25

if one wave (B) starts before another wave (A), we say that A is 90 deg out of phase with B or that B is -90 deg out of phase with A
- this is because B starts earlier than A

Question 26

out of phase half cycle

Answer 26

if one wave (C) starts after another wave (A), we say that A is -180 deg out of phase with C or that C is 180 deg out of phase with A
- this is because A starts earlier than

Question 27

out of phase three-quarter cycle

Answer 27

if one wave (B) starts before another wave (C), we say that B is 90 deg out of phase with C or that C is -90 deg out of phase with B
- this is because B starts earlier than C

Question 28

phase differences positive

Answer 28

If the phase difference between two waveforms of the same frequency is positive, we say that one wave LEADS the other

Question 29

phase differences negative

Answer 29

If the phase difference between two waveforms of the same frequency is negative, we say that one wave LAGS the other

Question 30

phase differences in an in phase sinusoidal

Answer 30

are the same shape and frequency the max and min points occur at the same time

Question 31

phase differences in an out of phase sinusoidal

Answer 31

are the same shape and frequency the max and min points for each waveforms occur at the different times

Question 32

when waveform A reaches its maximum value before waveform B reaches its maximum then ….

Answer 32

A leads B
- A reaches its 0 value and its minimum value first

Question 33

Phase lead

Answer 33

if one waveform reaches its max value before another waveform reaches its max value

Question 34

Phase lag

Answer 34

if one waveform reaches its max value after another waveform reaches its max value

Question 35

A & B
- in phase

Answer 35

amplitude doesn’t matter if peak and trough are same (both are sine waves)

Question 36

A & C
- C leads A (900 ) & A lags C

Answer 36

A is at peak when C is at 0 descending (C is a cosine wave)

Question 37

A & D
- A leads D (90 deg) & D lags A

Answer 37

A is at peak when D is at 0 ascending (d is a -cosine wave)

Question 38

B & C
- C leads B (90 deg) & B lags C

Answer 38

B is at peak when C is at 0 descending

Question 39

B & D
- B leads D (90 deg) & D lags B

Answer 39

B is at peak when D is at 0 ascending

Question 40

C & D
- C leads D & D lags C

Answer 40

Inverse
C is at peak when D is at trough and they cross at 0 (C= cosine(x) & D= - cosine(x))

Question 41

REMEMBER PHASE SHIFT DOES NOT CHANGE FREQUENCY, IT JUST MEANS…

Answer 41

TWO SIGNALS ARE AT DIFFERENT POINTS OF THEIR CYCLE AT A GIVEN TIME