Waves Flashcards

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1
Q

oscillation

A

back and forth motion

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2
Q

periodic

A

repetititive oscillation

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3
Q

period

A
  • time taken to complete one full oscillation
  • T
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4
Q

amplitude

A
  • maximum displacement of an oscillation from its equilibrium position
  • A
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5
Q

restoring force

A

force that brings the system back to its equilibrium position when the system is displaced away from its equilibrium

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6
Q

What is necessary for a system to oscillate?

A

restoring force

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7
Q

simple harmonic motion requirements

A
  • magnitude of acceleration of body that has been displaced from equilibrium is proportional to the displacement and direction of the acceleration towards the equilibrium
  • fixed equilibrium position
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8
Q

frequency

A

number of full oscillations per second

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9
Q

frequency equation

A

f = 1/T

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10
Q

graph showing the variation of displacement, velocity and acceleration in SHM

A
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11
Q

phase difference with graph representation

A

amount by which one curve is shifted forward relative to another curve

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12
Q

equation for phase difference

A

angle = shift/T x 360degrees

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13
Q

graph showing energy in SHM

A
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14
Q

wave

A
  • disturbance that travels in a medium
  • transfers energy and momentum from one place to another
  • direction of propagation of wave is direction of energy transfer
  • no large-scale motion of the medium itself as the wave passes through
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15
Q

superposition

A

when two or more waves of the same type arrive at point in space at same time displacement of medium is sum of individual displacements

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16
Q

wavelength

A

length of a complete oscillation

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17
Q
  1. crest
  2. trough
A
  1. highest point on the wave
  2. lowest point on the wave
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18
Q

transverse wave

A

displacement perpendicular to direction of energy transfer

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19
Q

longitudnal wave

A

displacement parallel to direction of energy transfer

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20
Q
  1. compression
  2. rarefaction
A
  1. areas of high pressure
  2. areas of low pressure
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21
Q

Can you tell the difference between transverse and longitudinal waves using a displacement-distance graph?

A

no - both look the same

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22
Q

diagram of an electromagnetic wave

  1. wavelength
  2. magnetic field
  3. electric field
A
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23
Q

At what speed do electromagnetic waves propagate in a vacuum?

A

speed of light

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24
Q

are electromagnetic waves longitudinal or transverse?

A

transverse

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25
Q

wavefronts

A
  • surface through crests
  • normal to direction of energy transfer
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26
Q

rays

A
  • lines perpendicular to wavefronts
  • show direction of wave propagation and energy transfer
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27
Q

What is the phase difference of wavefronts?

A

all points on wavefront have zero phase difference

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28
Q

diagram of wavefronts

  1. ray
  2. wavefronts
  3. wavelength
A
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29
Q

How are pulses reflected?

  1. On a fixed end
  2. On a loose end
A
  1. pulse exerts equal and opposite force on fixed end, so pulse is inverted when reflected
  2. reflected pulse not inverted because free to move
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30
Q

plane polarised

A

when electric field oscillates on the same plane

31
Q

polarisation with diagram

A

light is transmitted through certain media so all vibrations are limited to a single plane

32
Q

polariser with diagram

A

sheet of material with a molecular structure that only allows a specific orientation of the electric field to go through

33
Q

How to resolve components in a polariser?

A

vertical polarizer so only vertical component of electric field will go through

34
Q

What happens when horizontal and vertical polarizers are at right angles?

A

crossed polarisers transmit no light so when overlap appear black

35
Q

What happens when unpolarised light reflects off a non-metallic surface?

A

partially polarised - produces glare (horizontally polarised)

36
Q

law of reflection and diagram

A
  • angle of incidence is equal to angle of reflection
  • reflected and incident rays and normal lie on same plane (plane of incidence)
37
Q

Requirements for reflection to take place

A
  • reflecting surface must be sufficiently smooth
  • wavelength of incidence wave must be larger than size of irregularities on surface (=wavelength of reflected waves)
38
Q

refraction and diagram

A

travel of light from one medium to another where it has a different speed

changes direction of incident ray unless normal to boundary of media

39
Q

Snell’s law for light

A

n1sinO2 = n2sinO1

40
Q

refractive index equation

A

nm = c/cm

where nm is the refractive index of a medium

41
Q

dispersion

A

rays with the same angle of incidence but of different wavelength are refracted by different angles

42
Q

What causes white light to split up when passed through a prism?

A

dispersion of different wavelengths of light

43
Q

How does the wavelength, frequency and speed of a wave change when it passes to another medium?

A
  • frequency remains the same
  • speed changes (increases as wavelength increases)
  • wavelength changes (increases as speed increases)
44
Q

How does the wavelength affect the diffraction of a wave? Diagram

A

if wavelength small compared to gap: little diffraction

if wavelength large compared to gap: a lot of diffraction

45
Q

critical angle

A

angle of incidence for which the angle of refraction is 90 degrees

46
Q

total internal reflection with diagram

A
  • occurs when angle of incidence is greater than the critical angle
  • no refracted ray; just the reflected ray
47
Q

diffraction

A

spreading of a wave as it goes past an obstacle or through an aperture

48
Q

diagrams for diffraction around obstacle and edge

A
49
Q

double slit interference diagram

A

bright spots marked as n - indicates that path difference is n*wavelength

dark spots indicate that path difference is 1/2n*wavelength

50
Q

fringe spacing

A
  • distance on double slit screen between the middle of the bright spot and the middle of the next bright spot
  • symbol is s
51
Q

Which light has larger fringe spacing, red or green?

A

red because has longest wavelength

52
Q

standing (stationary) wave

A

wave in which the crests stay in the same place

53
Q

How is a standing wave formed?

A

when two waves of the same speed, wavelength and amplitude travelling in opposite directions meet

54
Q

What is the displacement of a standing wave compared to the original travelling waves?

A

sum of displacements of two travelling waves

55
Q

node

A

place on a wave where the displacement is always zero

56
Q

What is the wavelength of a standing wave?

A

distance between two consecutive nodes

57
Q

antinode

A

point where displacement of a standing wave is as large as possible

58
Q

Where are standing waves in phase?

A

points between consecutive waves

59
Q

What are the differences between standing waves and travelling waves?

A
  • standing waves do not transfer energy; travelling waves do
  • the amplitude of oscillation is different at different points on the standing wave; same on travelling wave
  • all points between two successive nodes on a standing wave are in phase; two neighbouring points on a travelling wave not in phase
60
Q

first harmonic

A

standing wave with longest wavelength and lowest frequency

61
Q

diagram showing patterns of increasing harmonics

  1. wavelength
  2. frequency
A
  1. decreases with increasing harmonic
  2. increases with increasing harmonic
62
Q

how do molecules move in a longitudinal standing wave in a pipe with antinode-antinode? diagram for first and second harmonics

A
  • molecules oscillate most at the ends (antinodes)
  • molecules do not oscillate in the middle (node)
63
Q

What is the first harmonic also called?

A

fundamental frequency (has lowest frequency)

64
Q

how to molecules move in a longitudinal standing wave in a node-node pipe? diagram for first and second harmonics

A
65
Q

how to molecules move in a longitudinal standing wave in a node-antinode pipe? diagram for first and second harmonics

A
66
Q

What type of wave is a standing wave in a tube?

A

longitudinal wave

67
Q

What is the wavelength of a standing wave?

A
68
Q

Intensity graph for single slit diffraction

A
69
Q

Intensity graph for double slit diffraction

A
70
Q

Effect on single slit diffraction pattern:

  1. if the width of the slit is reduced?
  2. if a red light source is replace with a green light source?
A
  1. Wider diffraction pattern; dimmer
  2. green light has smaller wavelength so narrower diffraction pattern with brighter central spot
71
Q
A
72
Q

Effect on double slit diffraction pattern if one narrow slit covered by opaque object?

A
  • large central fringe
  • side fringes narrower than central fringe
  • single slit diffraction pattern
73
Q

coherent source

A

source whose phase difference is constant in time and whose waves have the same frequency

74
Q

Why should single slit be narrow in single slit diffraction?

A

ensure wide diffraction