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physics > waves > Flashcards

waves Flashcards

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1
Q

how is a stationary wave formed

A

a wave is reflected causing 2 waves to travel in opposite directions with the same speed, frequency, and similar amplitude. a resultant wave is produced as a result of when the 2 waves superposition. total constructive interference at anti-nodes, maximum displacement. total deconstructive interference at nodes, minimum displacement

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2
Q

do stationary (standing) waves transfer or store energy

A

store energy. no energy is transferred

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3
Q

are stationary (standing) waves in phase or out of phase

A

in phase

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4
Q

real life applications of standing (stationary) waves?

A

musical instruments - formation of harmonics
telecommunications - used in antennas to maximise signal strength and minimise interference
medical imaging - used in ultrasound for images of internal organs

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5
Q

define coherence

A

sources are coherent if they maintain a fixed phase difference

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6
Q

define progressive wave

A

transmits energy

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7
Q

what is a critical angle

A

the angle of incidence causing the angle of refraction to be 90

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8
Q

what is total internal reflection

A

occurs inside a medium when a ray reflects back in
happens when angle of incidence larger than critical angle

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9
Q

what do fibre optics do

A

transmit information via light signals and total internal reflection

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10
Q

what are fibre optics made of

A

a core surrounded by cladding
made of glass or plastic

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11
Q

what does cladding in fibre optics do

A

protect the core from damage
prevents signal degradation = light escaping causing information to be lost

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12
Q

example of transverse wave

A

all electromagnetic
string
water

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13
Q

example of longitudinal wave

A

sound
ultrasound

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14
Q

what is signal degradation

A

when light escapes the optical fibre causing loss of information

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15
Q

causes of signal degradation

A

absorption
dispersion

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16
Q

what is absorption in an optical fibre

A

when some energy from the signal is absorbed by the fibre, decreasing its amplitude, losing some information

17
Q

what is dispersion in an optical fibre

A

dispersion causes pulse broadening which is when the received signal is broader than the original transmitted signal
broader signals can overlap so lose information

18
Q

what are the 2 types of dispersion

A

modal dispersion
material dispersion

19
Q

what is modal dispersion

A

when the light rays enter at different angles, so different paths, so different times to travel, causing pulse broadening

20
Q

what is material dispersion

A

when light rays are of different wavelengths, so different times to travel, causing pulse broadening

21
Q

how can modal dispersion be reduced

A

have the core of the fibre narrower so less difference between path taken

22
Q

how can material dispersion be prevented

A

use monochromatic light (light of one wavelength)

23
Q

how can both material and modal dispersion be reduced

A

use an optical fibre repeater
it regenerates the signal during travel

24
Q

define longitudinal waves

A

oscillations are parallel to the direction of energy transfer
made of compressions and rarefactions

25
Q

define transverse waves

A

oscillations are perpendicular to the direction of energy transfer

26
Q

what is a polarised wave

A

a wave that has oscillations that only travel in one plane
only transverse waves can be polarised

27
Q

how to be safe when using a laser

A

dont shine at person
dont shine at reflective materials
wear laser safety goggles
display warning sign

28
Q

what is the path difference of two waves when constructive interference occurs

A

nλ where n is an integer

29
Q

what is the path difference of 2 waves when destructive interference occurs

A

n+1/2 λ where n is an integer

30
Q

what is a diffraction grating

A

slide which has hundreds of slits per millimetre

31
Q

uses of a diffraction grating

A

x-ray crystallography
finding elements in stars

32
Q

how can the width of the central maxima in an interference pattern be changed

A

slit seperation
wavelength of light

33
Q

what does increasing slit separation do

A

decrease amount of diffraction that occurs, so make central maximum narrower and increase intensity

34
Q

what does increasing wavelength do

A

increase amount of diffraction that occurs because wavelength closer to size of slit, make central maximum wider and decrease intensity

35
Q

what does the interference pattern of white light look like

A

central maximum is white, with alternating light and dark besides it
violet is closest to the central maximum
red is furthest away from the central maximum because longest wavelength so diffracts more

36
Q

what experiment proves the wave nature of light

A

young’s double slit experiment

37
Q

how fast do electromagnetic waves travel in a vacuum

A

3x10^8 m/s

38
Q

lasers produce c___ and m____ light

A

coherent and monochromatic

39
Q

what does coherent light mean

A

same frequency, wavelength, phase difference

physics (6 decks)

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