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Physics > Topic 4 Waves > Flashcards

Topic 4 Waves Flashcards

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
intensity (I) definition
"power per unit area received by an observer" units: Wm^–2
26
the intensity of a wave is:
- 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
27
mechanical wave definition
mechanical waves require a medium through which to travel eg. sound and earthquake waves
28
electromagnetic wave definition
- 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
29
order of electromagnetic waves from low to high frequency (high to low wavelength)
Roman Men Invented Very Useful X-ray Guns => radio, microwave, infrared, visible, ultraviolet, x-rays, gamma
30
wavelengths of electromagnetic waves
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
31
what two things happen at the boundary when waves travel from one medium into another
- 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
32
name all the rays, angles etc. in a medium graph
incident ray normal reflected ray refracted ray angle of incidence (i) angle of reflection (r) medium 1/2 angle of refraction (r)
33
what happens when a waves goes from a faster medium to a slower one
bends towards the normal
34
what happens when a waves goes from a slower medium to a faster one
bends away from the normal
35
what happens when a waves enters a different medium at 90º
not change direction
36
snell's law
n = sin i ÷ sin r can only be used if the first medium is AIR
37
total internal reflection occurs when:
- 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
sin θc =
1/n1 (only is light is travelling from the medium INTO AIR)
39
what is a wavefront
a line connecting points on a wave with the same phase/displacement eg. |||||||| |||||||| ||||||||
40
what is a ray
- a line drawn to represent the direction a wave is travelling when viewed from above - rays are drawn at 90º to the wavefront |||||||| |||||||| ––––––––> ||||||||
41
how to draw reflected wavefronts
1. draw the normal 2. draw the reflected ray 3. draw the wavefronts at 90º to the reflected ray
42
how to draw refracted wavefronts
1. draw the normal 2. draw the refracted ray 3. draw the wavefronts at 90º to the refracted ray
43
what is diffraction
- 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
what is constructive interference
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
what is destructive interference
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
principle of superposition
"if two or more waves meet, the resultant displacement at any point is found by adding the displacements produced by each individual wave"
47
circular wave interference pattern
2 antinodal 1 nodal 1 antinodal 0 nodal 0 antinodal 0 nodal 1 antinodal 1 nodal 2 antinodal
48
antinodal lines
- waves meet in phase - constructive interference - path difference = nλ - maximum amplitude "maxima"
49
nodal lines
- waves meet out of phase - destructive interference - path difference = (n+1/2)λ - zero amplitude "minima"
50
light antinodal line and nodal line brightness level
antinodal: bright nodal: dark
51
sound antinodal line and nodal line loudness level
antinodal: loud nodal: quiet
52
double slit interference - young's experiment
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
standing waves form when:
- 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
fundamental frequency definition
lowest f at which a standing wave forms
55
how is a wave reflected at the open end
- as the air moves outwards it creates a low pressure region behind it that pulls the air back into the pipe
56
strings and pipes have a ______ of _______ ___________ (_________) at which they will form standing waves
strings and pipes have a range of resonant frequencies (harmonics) at which they will form standing waves
57
strings and open pipes can produce ____ ___________
strings and open pipes can produce all harmonics
58
closed pipes can only produce ____________ ___________
closed pipes can only produce odd-numbered harmonics
59
amplitude of standing waves
all points along the wave have different amplitudes. maximum amplitude at the antinodes, zero at the nodes
60
amplitude of travelling waves
all points along the wave have the same amplitude
61
wavelength of standing waves
λ is twice the distance from one node (or antinode) to the next node (or antinode)
62
wavelength of travelling waves
λ is the shortest distance between two points that are in phase
63
phase of standing waves
all points along the wave are moving in phase or 180º out of phase (except for the nodes which do not move)
64
phase of travelling waves
all points along the wave have different phases
65
energy of standing waves
energy is not transmitted by the wave but it doe posses energy
66
energy of travelling waves
energy is transmitted by the wave
67
frequency of standing waves
all points along the wave oscillate at the same frequency
68
frequency of travelling waves
all points along the wave oscillate at the same frequency
69
polarisation
- the oscillation of the medium is only in one plane - only transverse waves can be polarised
70
electromagnetic waves are made up of:
- oscillating electric and magnetic fields that are perpendicular to each other
71
definition of polarisation
the electric field vector is oscillating in one plane only
72
Brewster's Law
- 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
for polarised light, n=
n = tan ø
74
Malus' Law: polarising filter
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
Malus' Law: analyser
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
Malus' Law I = Io(cos θ)^2
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
if UNPOLARISED light passes through a polariser, the...
light intensity will be reduced by half
78
interference pattern occurs when
two waves must have the same plane of polarisation in order to produce an interference pattern
79
do waves of different planes of polarisation cancel or add or other
waves of different planes of polarisation cannot cancel out or add together - they create a wave of a different plane of polarisation
80
optically active substances
- sugar solutions - stress analysis - LCDs (liquid crystal displays) see pg 35 topic 4 booklet for how they work
81
optically active substances
- 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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