Waves and Sounds

Question 1

What is a sinusoidal waves?

Answer 1

the individual particles oscillate back and forth with a displacement that follows a sinusoidal pattern; sin wave

Question 2

What are transverse waves?

Answer 2

waves in which the direction of particle oscillation in perpendicular to the propagation; imagine a wave in a stadium, people standing up and down but not moving sideways

Question 3

What are examples of transverse waves?

Answer 3

electromagnetic waves, visible light, microwaves, x rays

Question 4

What are longitudinal waves?

Answer 4

waves in which the particles of the wave oscillate parallel to the direction of propagation; in the direction of energy transfer

Question 5

What are examples of longitudinal waves?

Answer 5

sound waves

Question 6

What is a crest on a sound wave?

Answer 6

the top point or maximum

Question 7

What is a wavelength?

Answer 7

(lambda) the distance from one crest to another

Question 8

What is frequency?

Answer 8

(f) number of wavelengths passing a fixed points per second

Question 9

What is the units for frequency?

Answer 9

Hz/cycles per second (cps)

Question 10

What is the propagation speed equation?

Answer 10

v = frequency * wavelength

Question 11

What is a period?

Answer 11

(T) - the number of seconds per wavelength cycles

Question 12

What is the equation for angular frequency?

Answer 12

w = 2*pi*f = 2*pi/T
w = angular frequency
f = frequency
T = period

Question 13

What is the equilibrium point?

Answer 13

a central point about which waves oscillate

Question 14

What is amplitude?

Answer 14

(A) the maximum magnitude of displacement of the wave - so length from equilibrium point to either crest or trough

Question 15

What is phase differences?

Answer 15

a way to describe two waves relative to each other - in phase is when the respective troughs and crests decline; out of crest is the opposite

Question 16

Principle of Superposition

Answer 16

when waves interact with each other, the displacement of the resultant wave at any point is the sum of the displacements of the two interacting waves

Question 17

What is constructive interference?

Answer 17

the waves are perfectly in phase, the displacements always add together and the amplitude of the resultant is equal to the sum of the amplitudes of the two waves

Question 18

What is destructive interference?

Answer 18

when the waves are perfectly out of phase, the displacements always counteract each other and the amplitude of the resultant wave is the difference between the amplitudes of the interacting waves

Question 19

What are nodes?

Answer 19

points on the wave that remain at rest

Question 20

What are antinodes?

Answer 20

points midway between the nodes fluctuate with maximum amplitude

Question 21

What is timbre?

Answer 21

quality of sound; determined by the natural frequency of the object

Question 22

What is sound?

Answer 22

a longitudinal wave transmitted by the oscillation of particles in a deformable medium

Question 23

What is the equation for speed of sound?

Answer 23

v = sqrt(B/p)
B = medium's resistance to compression
p = density of the medium

Question 24

What is pitch?

Answer 24

our perception of the frequency of sound; lower frequency = lower pitch

Question 25

What are infrasonic waves?

Answer 25

sound waves with frequencies below 20 Hz

Question 26

What are ultrasonic waves?

Answer 26

sound waves with frequencies above 20,000 Hz

Question 27

What is the Doppler effect?

Answer 27

describes the difference between the actual frequency of a sound and its perceived frequency when the source of the sound and the sounds detector are moving relative to one another

Question 28

What is the equation for the Doppler effect?

Answer 28

f' = f[(v +- vD)/(v-+ vS)]
f' = perceived frequency
f = actual emitted frequency
v = speed of sound in the medium
vD = speed of the detector
vS = speed of source 
Top sign when detector is moving towards the object
Bottom sign when moving away

Question 29

What is echolocation?

Answer 29

emitting the sound serves as both the source and detector of the sound; the time it takes for the sound to return and the change in frequency can be used to determine positions of objects

Question 30

What is a shock wave?

Answer 30

a moving object travels at a high speed that allows wave fronts to build upon each another in front of the object, increasing amplitude and thus compression/pressure

Question 31

What is a sonic boom?

Answer 31

the passing of the shock wave which goes from high pressure to very low pressure

Question 32

What is loudness/volume?

Answer 32

the way we perceive its intensity

Question 33

What is the equation for intensity?

Answer 33

I = P/A
I = intensity
P = power
A = area

Question 34

What are the units for intensity?

Answer 34

watts per square meter (W/m^2)

Question 35

What is the equation for sound level?

Answer 35

B = 10log(I/I0)
B = sound wave
I = intensity of the sound wave
I0 = threshold of hearing (1x10-12 W/m^2)

Question 36

What is the equation for change in sound level?

Answer 36

Bfinal = Binitial + 10 log (Ifinal/Iinitial)

Question 37

What is the equation for wavelength?

Answer 37

lambda = 2L/n
L = length of the strength
n = number of nodes (harmonic)

Question 38

What is the equation for frequency?

Answer 38

f = velocity of wave speed/lambda