Chapter 14 - Waves

Front 1

What is a wave?

Back 1

A disturbance in space.

Front 2

A wave carries:
A) Energy
B) Mass
C) A and B
D) None of the above

Back 2

A) Energy

Front 3

The energy of a wave is proportional to what?

Back 3

Amplitude squared

Front 4

Any wave can be simplified into which functions?

Back 4

sine and cosine

Front 5

The maximum point of a wave is called a what?

Back 5

Crest

Front 6

The minimum point of a wave is called a what?

Back 6

Trough

Front 7

Amplitude is measured from where to where?

Back 7

From center line to crest, or from center line to trough

Front 8

Wavelength is represented by what symbol?

Back 8

λ (Lambda)

Front 9

Wavelength is measured from where to where? (assuming x is distance)

Back 9

Distance between two crests, or two troughs (alternatively, two nodes and two antinodes)

Front 10

Frequency is what?

Back 10

Number of cycles/revolutions per second

Front 11

What is the equation for frequency?

Back 11

f = 1/T (f is frequency, T is period)

Front 12

Period is measured from where to where? (assuming x is time)

Back 12

Distance between two crests, or two troughs (alternatively, two nodes and two antinodes)

Front 13

The speed of any wave is what?

Back 13

v = λf or v = λ/T
speed = wavelength * frequency

Front 14

The speed of a wave depends on what two external conditions?

Back 14

Medium and temperature

Front 15

What is the equation for the speed of sound?

Back 15

Vsound = 331.4 + 0.6Tc
Vsound is speed of sound, Tc is temperature in Celsius

Front 16

The speed of sound at STP is what?

Back 16

331.4 + 0.6(0) = 331.4 m/s

Front 17

The speed of sound is fastest in what?

Back 17

Solid (especially metal), followed by liquid, followed by gas

Front 18

Why does a solid propagate fastest in a solid?

Back 18

A solid is denser, the molecules are closer and so they can carry more energy.

Front 19

Sound cannot propagate in a _______________ because it requires a _______________ to propagate.

Back 19

Sound cannot propagate in a VACUUM because it requires a MEDIUM to propagate.

Front 20

The speed of light is fastest in what?

Back 20

A vacuum, followed by a gas, followed by a liquid, and so on.

Front 21

Why does light slow down in denser materials?

Back 21

Light does not need a medium to transfer energy, and so it scatters when it hits molecules.

Front 22

What is the speed of sound at room temperature?

Back 22

343 m/s

Front 23

What is the speed of light or any EM wave in a vacuum or air (the difference of a vacuum and air is negligible)

Back 23

3*10^8 m/s (3e8 m/s)

Front 24

What are the two types of waves in regards to oscillation?

Back 24

Longitudinal and transverse

Front 25

The oscillation of a longitudinal wave is in which direction?

Back 25

The direction of propagation

Front 26

The oscillation of a transverse wave is in which direction?

Back 26

Perpendicular to the direction of propagation

Front 27

Sound is what type of wave?

Back 27

Longitudinal

Front 28

Light and other EM waves are what type of wave?

Back 28

Transverse

Front 29

What is the mathematical form of a wave?

Back 29

y = Asin[kx-wt] or y=Acos[kx-wt]
y can also be written as f(x,t)

Front 30

What does the k mean in the mathematical form of a wave?

Back 30

The wave number, it is equivalent to (2 * pi) / wavelength

Front 31

What does the w mean in the mathematical form of a wave?

Back 31

The angular frequency, it is equivalent to 2 * pi * f

Front 32

What is the unit of k in the mathematical form of a wave?

Back 32

1/m or m^-1

Front 33

What is the unit of w in the mathematical form of a wave?

Back 33

1/s or s^-1

Front 34

What two variables are left untouched in the creation of the mathematical form of a wave?

Back 34

x and t, representing displacement and time

Front 35

All EM waves have the same what?

Back 35

Speed, 3*10^8 m/s

Front 36

A wave will travel further if it has a bigger what?

Back 36

Wavelength, it will collide less and be able to overcome more collisions.

Front 37

Wavelength is ________ proportional to frequency.

Back 37

Inversely

Front 38

Wavelength is ___________ proportional to energy.

Back 38

inversely

Front 39

Energy is _____________ proportional to frequency

Back 39

directly

Front 40

Visibile light is between what two wavelengths?

Back 40

400nm and 700nm

Front 41

The wavelength of blue light is what?

Back 41

Around 450nm

Front 42

The wavelength of red light is what?

Back 42

Around 700nm

Front 43

Electric field is due to what?

Back 43

The oscillation of the charge of the electrons

Front 44

Magnetic field is due to what?

Back 44

Electron spin

Front 45

All EM waves come from electrons expect which?

Back 45

Gamma rays

Front 46

Gamma rays come from what?

Back 46

The nucleus

Front 47

X-ray, infared, microwave, visible light, UV ray, gamma ray, radio wave. Order those in terms of increasing wavelength (smallest to largest).

Back 47

Gamma ray, X-ray, UV, visible light, IR, microwave, radio wave.

Front 48

X-ray, infared, microwave, visible light, UV ray, gamma ray, radio wave. Order those in terms of increasing frequency (smallest to larges).

Back 48

Radio wave, microwave, IR, visible light, UV, X-ray, gamma ray

Front 49

All EM waves consist of what?

Back 49

Massless particles called photons.

Front 50

What is the energy of a single photon?

Back 50

hf or (hc)/wavelength, h is Planck's constant, f is frequency, c is the speed of light

Front 51

The symbol for an electric field is

Back 51

E

Front 52

The symbol for a magnetic field is

Back 52

B

Front 53

Describe the relationship between E field, B field, and the propagation of a wave.

Back 53

They are perpendicular.

Front 54

The superposition principle applies when two waves are what?

Back 54

Passing through a medium at the same moment

Front 55

What is the resultant (net) of all waves?

Back 55

The sum of all individual waves

Front 56

What two types of interferences are there?

Back 56

Constructive and destructive

Front 57

Constructive interferences occurs when two waves are what?

Back 57

In phase, there is 0 degrees between them, max meets max, min meets min

Front 58

Destructive interference occurs when two waves are what?

Back 58

Out of phase, 180 degrees between them, max meets min, min meets max.

Front 59

When two waves are equal but undergo destructive interference, what is ynet?

Back 59

0

Front 60

Standing waves are what?

Back 60

Two waves that have the same amplitude, wavelength, and frequency but are propagating in opposite directions, resulting in a wave that does not move anywhere.

Front 61

Waves are directed outwards in what shape?

Back 61

Spherical

Front 62

Distance and intensity are __________ proportional

Back 62

Inversely

Front 63

Intensity is equal to what?

Back 63

Power over area, P/A, or more specifically, (P / (4 * pi * r^2))

Front 64

What is the surface area of a sphere?

Back 64

4 * pi * r^2

Front 65

Intensity is directly proportional to what?

Back 65

1/r^2

Front 66

What is the unit of intensity?

Back 66

Watts / m^2

Front 67

Audible sound is between what two frequencies?

Back 67

20Hz and 20kHz (20Hz and 20,000Hz)

Front 68

Sound that is lower than 20Hz is called what?

Back 68

Infrasonic

Front 69

Sound that is higher than 20kHz is called what?

Back 69

Ultrasonic

Front 70

What is intensity level?

Back 70

β = 10Log(I/Io)
β is intensity level, I is intensity, Io is reference intensity (threshold of hearing)

Front 71

Intensity level compares what two things?

Back 71

Intensity with reference intensity (threshold of hearing)

Front 72

What is the reference intensity?

Back 72

The threshold of human hearing, Io = 10^-12 W/m^2

Front 73

What unit does β have?

Back 73

β has no unit, it is a dimensionless quantity. We use dB to represent the unit.

Front 74

What is the difference between two intensity levels?

Back 74

∆β = |10Log(I2/I1)|

Front 75

Is intensity scalar or vector?

Back 75

Scalar

Front 76

What is the net intensity at a certain point?

Back 76

The sum of all intensities, Inet = I1 + I2 + ...

Front 77

The speed of a wave on a string/rope/cable depends on which two quantities?

Back 77

1) The tension (force) in the string, Ft or simply T.
2) The mass density of the string, the mass per unit length, μ

Front 78

What is the mass density of a string?

Back 78

μ = M/L, where μ is mass density, M is mass of the string, and L is length of the string

Front 79

What is the speed of a wave on a string?

Back 79

v = sqrt(T/μ), T is tension, μ is mass density (aka M/L)

Front 80

For μ, M and L apply only to which parts of the string?

Back 80

The parts that form the wave.

Front 81

The speed of a wave on a string is faster if:

Back 81

1) The mass density is lower
2) The tension is greater

Front 82

What are the nodes of a wave?

Back 82

The parts of the wave where amplitude is 0 and it does not move up and down with time.

Front 83

Where are the antinodes of a wave?

Back 83

The maximum or minimum points of that wave in regards to amplitude.

Front 84

When will two systems resonate?

Back 84

When they have the same frequency (and thus form a standing wave)

Front 85

The resonance frequency of a system is what?

Back 85

The frequency at which a system will oscillate with greater amplitude.

Front 86

What is the beat frequency?

Back 86

An interference of two sounds with slightly different frequencies.

Front 87

How do you calculate beat frequency?

Back 87

fbeat = |f2 - f1| (assuming f2 and f1 are reasonable close)

Front 88

What is the Doppler Effect?

Back 88

The shift in wavelength or frequency due to the movement of the source or listener.

Front 89

If a source is moving towards a listener, that listener will perceive what change in frequency and wavelength?

Back 89

A higher frequency and a shorter wavelength.

Front 90

If a source is moving away from a listener, that listener will perceive what change in frequency and wavelength?

Back 90

A lower frequency and a longer wavelength.

Front 91

What is the name given to the increase in wavelength of light due to the Doppler Effect?

Back 91

Red-shift

Front 92

What is the name given to the decrease in wavelength of light due to the Doppler Effect?

Back 92

Blue-shift

Front 93

To hear a sound from a bottle, where must the nodes and antinodes be located?

Back 93

The node must be at the bottom of the bottle, and the antinode must be at the top of the bottle.

Front 94

The length of a bottle must be equal to what in order to form a standing wave?

Back 94

L = wavelength / 4.

Front 95

After two waves interfere, what happens when they pass?

Back 95

They preserve their original, individual wave amplitudes.

Front 96

Important formulas to memorize:

1) Speed of a wave
2) Frequency of a wave
3) Speed of sound
4) Mathematical definition of a wave
5) Wave number
6) Angular frequency
7) Energy of a single photon
8) Intensity
9) Intensity level (compared to reference intensity)
10) Change in intensity level
11) Speed of a wave on a string
12) Mass density of a string
13) Beat frequency

Back 96

1) v = λf
2) f = 1/T
3) vsound = 331.4 + 0.6Tc
4) y=Acos(kx-wt) or y=Asin(kx-wt)
5) k = 2π/λ
6) w = 2πf
7) E = hf or E = hc/λ
8) I = P/A or I = P/4π(r^2)
9) β = 10Log(I/Io)
10) ∆β = |10Log(I2/I1)|
11) V = sqrt(T/µ)
12) µ = M/L
13) fbeat = |f2-f1|

Front 97

Important constants to memorize:

1) Speed of sound at STP
2) Speed of sound at room temp
3) Speed of light or any EM wave
4) Red wavelength (upper wavelength limit for visible light)
5) Blue wavelength ("lower" wavelength limit for visible light, although violet is lower than blue)
6) Lower frequency limit of sound
7) Upper frequency limit of sound
8) Reference intensity (threshold of hearing)

Back 97

1) 331.4 m/s
2) 343 m/s
3) 3 * 10^8 m/s
4) 700nm
5) 450nm (violet is 400nm - 450nm)
6) 20Hz
7) 20kZ (20000 Hz)
8) 10^-12 W/m^2