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Physics > Topic 4 Waves > Flashcards

Topic 4 Waves Flashcards

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1
Q

oscillation definition

A

a back and forth motion about an equilibrium position

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2
Q

isochronous definition

A

an oscillation that repeats with the same time period

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3
Q

displacement (x) oscillations definition

A

instantaneous distance from the equilibrium position in a specific direction (m)

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4
Q

amplitude (xo) oscillations definition

A

maximum displacement from the equilibrium position (m)

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5
Q

frequency (f) oscillations definition

A

number of oscillations per second (Hz or s^–1)

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6
Q

period (T) oscillations definition

A

time for one oscillation (s)

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7
Q

phase (ø) oscillations definition

A

measure of how “in step” different particles are (one cycle = 360º or 2π radians)

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8
Q

simple harmonic motion (SHM) definition

A

a type of oscillation that takes place when the acceleration of (and the force on) an object is:
- proportional to its displacement from the equilibrium position
- in the opposite direction to the displacement (ie. directed towards the equilibrium position)

the motion is due to a restoring force, ie. a force that is always directed towards the equilibrium position.

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9
Q

acceleration against displacement graph for oscillation

A
  • straight line shows that a∝x
  • negative gradient shows a and x are in opposite directions
    see pg 5 topic 4 booklet for picture
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10
Q

acceleration time graphs

A

see pg 8 topic 4 booklet for graphs

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11
Q

energy in shm graphs

A

see pg 9 topic 4 booklet for graphs

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12
Q

what is a wave

A

a movement of energy through a medium

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13
Q

longitudinal wave definition

A

the particles of the medium vibrate parallel to the direction of the energy transfer (energy prorogation) eg. sound, earthquake P waves

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14
Q

transverse wave definition

A

the particles of the medium vibrate at right angles to the direction of the energy transfer eg. light, earthquake S waves

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15
Q

compression

A

particles come together

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16
Q

rarefaction

A

particles spread out

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17
Q

displacement (x) wave definition

A

distance the medium had moved from the equilibrium position in a particular direction
unit: m

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18
Q

frequency (f) wave definition

A

number of oscillation of the medium (or complete waves passing a point) per second
unit: Hz

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19
Q

period (T) wave definition

A

time for one complete oscillation of the medium (or time for one complete wave to pass a given point)
unit: s

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20
Q

wavelength (λ) wave definition

A

shortest distance between two points that are in phase along a wave eg. crest to crest
unit: m

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21
Q

wave speed (c) wave definition

A

distance travelled per unit time by the energy of the wave (or by a wavefront)
unit: ms^–1

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22
Q

amplitude (A) wave definition

A

maximum displacement of the medium from the equilibrium position
unit: m

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23
Q

properties of waves

A

see pg 12/13 topic 3 booklet

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24
Q

derive the formula that shows the relationship between wave speed, wavelength and frequency

A
  • time taken for one complete wave to pass = T
  • the distance the wave has travelled in this time = λ
  • wave speed (c) = distance / time = λ/T
  • but T = 1/f
    therefore:
  • c = λ/f
  • => c = fλ
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25
Q

intensity (I) definition

A

“power per unit area received by an observer”
units: Wm^–2

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26
Q

the intensity of a wave is:

A
  • proportional to the square of the amplitude (A) of the wave I∝A^2
  • inversely proportional to the square of the distance (x) from the source I∝x^–2
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27
Q

mechanical wave definition

A

mechanical waves require a medium through which to travel
eg. sound and earthquake waves

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28
Q

electromagnetic wave definition

A
  • electromagnetic waves do not require a medium so they are able to travel through a vacuum
  • eg. visible light and radio waves
  • all electronegative waves are transverse and travel at 3.00x10^8 ms^–1 in a vacuum
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29
Q

order of electromagnetic waves from low to high frequency (high to low wavelength)

A

Roman Men Invented Very Useful X-ray Guns
=> radio, microwave, infrared, visible, ultraviolet, x-rays, gamma

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30
Q

wavelengths of electromagnetic waves

A

radio: 10^2 m
microwave: 10^–3 m
infrared: 10^–5 m
visible: 10^–7 m
ultraviolet: 10^–9 m
x-ray: 10^–12 m
gamma: 10^–14 m

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31
Q

what two things happen at the boundary when waves travel from one medium into another

A
  • some of the wave’s energy will be reflected
  • some of the wave’s energy will enter the medium but will change speed - this change in speed is called refraction
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32
Q

name all the rays, angles etc. in a medium graph

A

incident ray
normal
reflected ray
refracted ray
angle of incidence (i)
angle of reflection (r)
medium 1/2
angle of refraction (r)

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33
Q

what happens when a waves goes from a faster medium to a slower one

A

bends towards the normal

34
Q

what happens when a waves goes from a slower medium to a faster one

A

bends away from the normal

35
Q

what happens when a waves enters a different medium at 90º

A

not change direction

36
Q

snell’s law

A

n = sin i ÷ sin r

can only be used if the first medium is AIR

37
Q

total internal reflection occurs when:

A
  • light is travelling from a more to a less optically dense medium (ie. it is speeding up/n is getting smaller)
  • the angle of incidence at the boundary is greater than the critical angle (θc)
38
Q

sin θc =

A

1/n1
(only is light is travelling from the medium INTO AIR)

39
Q

what is a wavefront

A

a line connecting points on a wave with the same phase/displacement
eg.
||||||||
||||||||
||||||||

40
Q

what is a ray

A
  • a line drawn to represent the direction a wave is travelling when viewed from above
  • rays are drawn at 90º to the wavefront

||||||||
||||||||
––––––––>
||||||||

41
Q

how to draw reflected wavefronts

A
  1. draw the normal
  2. draw the reflected ray
  3. draw the wavefronts at 90º to the reflected ray
42
Q

how to draw refracted wavefronts

A
  1. draw the normal
  2. draw the refracted ray
  3. draw the wavefronts at 90ºto the refracted ray
43
Q

what is diffraction

A
  • when waves move past an obstacle or through a gap the waves tend to spread out
  • longer wavelengths diffract more
  • if gap width = wavelength, circular wavefronts are produced
  • amplitude will decrease as the energy is spread out over a longer wavefront
44
Q

what is constructive interference

A

if the waves meet in phase they will form a resultant wave with an amplitude equal to the sum of the two individual waves

the superposition is twice the height

45
Q

what is destructive interference

A

if the waves meet out of phase they will cancel each other our to give a wave of zero amplitude (assuming both waves are of equal amplitude)

the superposition is canceled out

46
Q

principle of superposition

A

“if two or more waves meet, the resultant displacement at any point is found by adding the displacements produced by each individual wave”

47
Q

circular wave interference pattern

A

2 antinodal
1 nodal
1 antinodal
0 nodal
0 antinodal
0 nodal
1 antinodal
1 nodal
2 antinodal

48
Q

antinodal lines

A
  • waves meet in phase
  • constructive interference
  • path difference = nλ
  • maximum amplitude “maxima”
49
Q

nodal lines

A
  • waves meet out of phase
  • destructive interference
  • path difference = (n+1/2)λ
  • zero amplitude “minima”
50
Q

light antinodal line and nodal line brightness level

A

antinodal: bright
nodal: dark

51
Q

sound antinodal line and nodal line loudness level

A

antinodal: loud
nodal: quiet

52
Q

double slit interference - young’s experiment

A
  1. ‘light source’ shining through a ‘double slit’ where the distance between the slits is ‘d’
    - ‘diffraction’ occurs when the light passes through the slit
    - the light ‘interferes’ with each other and creates an ‘interference pattern’
    - dark and bright ‘fringes’ are seen
    - s = λD/d
    where:
    - s is the distance between the bright fringes
    - λ is wavelength of the light
    - d is the distance between the double slits
    - D is the distance from the double slits to interference pattern on a screen
    and all distances are in meters
53
Q

standing waves form when:

A
  • two waves of the same type meet and they must be:
  • of the same amplitude
  • of the same frequency
  • travelling in opposite directions

they only form if the λ fits the string

54
Q

fundamental frequency definition

A

lowest f at which a standing wave forms

55
Q

how is a wave reflected at the open end

A
  • as the air moves outwards it creates a low pressure region behind it that pulls the air back into the pipe
56
Q

strings and pipes have a ______ of _______ ___________ (_________) at which they will form standing waves

A

strings and pipes have a range of resonant frequencies (harmonics) at which they will form standing waves

57
Q

strings and open pipes can produce ____ ___________

A

strings and open pipes can produce all harmonics

58
Q

closed pipes can only produce ____________ ___________

A

closed pipes can only produce odd-numbered harmonics

59
Q

amplitude of standing waves

A

all points along the wave have different amplitudes. maximum amplitude at the antinodes, zero at the nodes

60
Q

amplitude of travelling waves

A

all points along the wave have the same amplitude

61
Q

wavelength of standing waves

A

λ is twice the distance from one node (or antinode) to the next node (or antinode)

62
Q

wavelength of travelling waves

A

λ is the shortest distance between two points that are in phase

63
Q

phase of standing waves

A

all points along the wave are moving in phase or 180º out of phase (except for the nodes which do not move)

64
Q

phase of travelling waves

A

all points along the wave have different phases

65
Q

energy of standing waves

A

energy is not transmitted by the wave but it doe posses energy

66
Q

energy of travelling waves

A

energy is transmitted by the wave

67
Q

frequency of standing waves

A

all points along the wave oscillate at the same frequency

68
Q

frequency of travelling waves

A

all points along the wave oscillate at the same frequency

69
Q

polarisation

A
  • the oscillation of the medium is only in one plane
  • only transverse waves can be polarised
70
Q

electromagnetic waves are made up of:

A
  • oscillating electric and magnetic fields that are perpendicular to each other
71
Q

definition of polarisation

A

the electric field vector is oscillating in one plane only

72
Q

Brewster’s Law

A
  • reflection off a surface
  • it will be polarised in the place of the surface
  • eg. if it reflects of a horizontal surface it will be polarised horizontally

see pg 33 topic 4 booklet for diagram

73
Q

for polarised light, n=

A

n = tan ø

74
Q

Malus’ Law:
polarising filter

A

a polarising filter polarises light

(it is made up of chain crystals embedded in a transparent film. the polaroid restricts the electric field vector of electromagnetic waves passing through it to a direction perpendicular to the chains)

75
Q

Malus’ Law:
analyser

A

a device that can detect polarised light

(analysers allow through components of polarised light in a preferred direction. If the angle between the polarisation of the incident light and the preferred direction is 0º to 90º then some light will pass through. if the angle = 90º then no light passes through)

76
Q

Malus’ Law
I = Io(cos θ)^2

A

I = intensity of transmitted light (W m^–2)
Io = intensity of incident light (W m^–2)
θ = angle between plane of polarisation of incident light and the analyser’s preferred direction

77
Q

if UNPOLARISED light passes through a polariser, the…

A

light intensity will be reduced by half

78
Q

interference pattern occurs when

A

two waves must have the same plane of polarisation in order to produce an interference pattern

79
Q

do waves of different planes of polarisation cancel or add or other

A

waves of different planes of polarisation cannot cancel out or add together - they create a wave of a different plane of polarisation

80
Q

optically active substances

A
  • sugar solutions
  • stress analysis
  • LCDs (liquid crystal displays)

see pg 35 topic 4 booklet for how they work

81
Q

optically active substances

A
  • sugar solutions
  • stress analysis
  • LCDs (liquid crystal displays)

see pg 35 topic 4 booklet for how they work

Physics (13 decks)

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