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waves Flashcards

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1
Q

what is a progressive wave?

A

a wave that transfers energy from one point to another without transferring matter

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2
Q

define displacement of a wave

A

how far a point on a wave has moved from its equilibrium

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3
Q

define amplitude of a wave

A

maximum magnitude of the displacement

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4
Q

define wavelength of a wave

A

the distance between neighbouring points on two waves

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5
Q

define period of a wave

A

time taken for a whole cycle to complete

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6
Q

define frequency of a wave

A

number of cycles per second passing a given point

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7
Q

define phase of a wave

A

measurement of the position of a certain point along the wave cycle

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8
Q

define phase difference

A

the amount one wave lags behind another

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9
Q

how can you work out the frequency of a wave?

A

f=1/time period

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10
Q

give the wave equation

A

v= fλ

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11
Q

what does an oscilloscope do?

A

displays waves from a signal generator as a function of voltage over time

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12
Q

what is a transverse wave?

A

a wave where oscillations are perpendicular to the direction of energy transfer

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13
Q

give an example of a transverse wave

A

electromagnetic waves

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14
Q

what is a longitudinal wave?

A

a wave where oscillations are parallel to the direction of energy transfer

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15
Q

give a similarity and difference between a transverse and longitudinal wave

A

similarity- both transfer energy

difference- transverse have peaks/troughs whereas longitudinal have compressions and rarefactions

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16
Q

give an example of a longitudinal wave

A

sound waves

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17
Q

what is intensity?

A

rate of flow of energy per unit area at right angles to the direction of travel of the wave

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18
Q

give the intensity equation

A

I=power/area

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19
Q

what is the relationship between intensity and amplitude

A

intensity is directly proportional to amplitude squared

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20
Q

give a property of all EM waves

A

all travel at speed of light (3.8x10^8) in a vacuum

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21
Q

what are EM waves?

A

transverse waves that consist of vibrating magnetic and electric fields at right angles to each other and direction of travel

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22
Q

give a use of radio waves

A

radio transmission

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23
Q

give a use of microwaves

A

cooking
radar
tv transmissions

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24
Q

give a use of infrared radiation

A

heat detectors
night vision cameras
optical fibres

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25
Q

give a use of visible light

A

human sight

optical fibres

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26
Q

give a use of ultraviolet light

A

sunbeds

security

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27
Q

give a use of x-rays

A

see damage to bones and teeth
airport security scanners
kill cancer cells

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28
Q

give a use of gamma rays

A

kill cancer cells

sterilisation of medical equipment

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29
Q

give the EM spectrum in order of increasing frequency and decreasing wavelength

A 
radiowaves
microwaves
infrared radiation
visible light
ultraviolet
x-rays
gamma rays
30
Q

what is a polarised wave?

A

a wave that only oscillates in one direction

31
Q

what is the plane of polarisation?

A

the plane in which a wave vibrates in

32
Q

what is plane polarisation?

A

polarising a wave so it only oscillates in one direction

33
Q

how can a wave be polarised?

A

using a polarising filter that only transmits vibrations in one direction

34
Q

can longitudinal waves be polarised?

A

no, only transverse waves can

35
Q

how can you polarise microwaves?

A

using metal grilles - polarising filters won’t work

36
Q

describe why the intensity of microwaves drops to 0 when the wires of the metal grille are aligned with the direction of the microwaves

A
  • the vibrating electric field of the microwave excites electrons in the metal grille
  • energy of incoming microwaves is absorbed and re-emitted in all directions
  • only a few re-emitted waves are vibrating in direction of microwave receiver
  • only microwaves in one plane are received
  • when wires and vibrations of the waves are aligned, more electrons are excited that when the grille and vibration of the waves are at right angles to each other- causes drop in intensity
37
Q

define diffraction

A

the spreading out of waves as they pass through a narrow gap or go round an obstacle

38
Q

what does the amount of diffraction depend on?

A

size of the gap compared to the λ

39
Q

when do you get the most diffraction?

A

when the gap is the same size as the wavelength

40
Q

how can you demonstrate diffraction in light using laser light?

A

-shining light through a narrow slit onto a screen. you can alter amount of diffraction by changing the width of the slit

or

-use a white light source and a set of coloured filters to see how wavelength varies for each colour and how diffraction changes

41
Q

what does the diffraction pattern look like when the wavelength of a light wave is similar to the size of the slit?

A

pattern of light and dark fringes are seen

42
Q

what is reflection of a wave?

A

wave is bounced back when it hits a boundary.

angle of incidence = angle of reflection

43
Q

what is refraction of a wave?

A

wave changes direction when entering a different medium as a result of the wave slowing down or speeding up

44
Q

if a wave slows down, does the wave bend towards or away from the normal?

A

towards

45
Q

if a wave speeds up, does the wave bend towards or away from the normal?

A

away

46
Q

what is the refractive index of a material?

A

measure of how much a material slows down light

47
Q

define the absolute refractive index of a material

A

the ratio between the speed of light in a vacuum and the speed of light in that material

48
Q

what is the equation for refractive index?

A

n=c/v

49
Q

what is the refractive index of air?

A

1

50
Q

what equation is given for a light ray passing across a boundary between 2 materials?

A

nsinθ = constant

51
Q

give Snell’s law

A

n1sinθ1 = n2sinθ2

52
Q

when the angle os refraction is 90 degrees, what is the angle of incidence?

A

critical

53
Q

what is total internal reflection?

A

when all light is reflected back into the material

54
Q

how can you find the critical angle?

A

sinC= 1/n

55
Q

define superposition

A

when two or more waves pass through each other

56
Q

give the principle of superposition

A

when two or more waves, cross, the resultant displacement equals the vector sum of the individual displacements

57
Q

what are the two types of interference?

A

constructive and destructive

58
Q

explain constructive interference

A

two points on a wave meet to create a larger displacement. e.g crest + crest gives a bigger crest

59
Q

explain destructive interference

A

two points on a wave meet to give no displacement

e.g crest + trough meet to give nothing

60
Q

describe what is meant when a wave is ‘in phase’

A
  • points on adjacent waves on at the same position, have the same displacement and velocity
  • two points in phase interfere constructively
  • phase difference of 0 or a multiple of 360 degrees is in phase (2pi)
61
Q

describe what is meant when a wave is ‘out of phase’

A
  • points on adjacent waves that are not in the same position, have different displacements and different velocities
  • phase difference of odd number multiples of 180 (pi radians)
62
Q

how can you get interference patterns from two sources?

A

the two sources must be coherent

63
Q

define coherent

A

same wavelength
same frequency
fixed phase difference

64
Q

what does constructive or destructive interference depend on?

A

path difference

65
Q

when would constructive interference occur?

A

when path difference = nλ (n=integer)

66
Q

when would destructive interference occur?

A

when path difference = (2n+1)λ/2

or (n+0.5)λ

67
Q

how can you demonstrate interference for EM radiation?

A

Young’s double slit experiment

68
Q

describe Young’s double slit experiment

A

-laser light is coherent and monochromatic
-slits must be same size as wavelength of laser light so it is diffracted
-pattern of light and dark fringes is created depending on whether constructive or destructive interference occurs
-work out wavelength with Young’s double slit formula
fringe spacing, x = λD/a

69
Q

does young’s experiment support the wave or particle model of light?

A

wave

70
Q

what other practical can be used to work out the wavelength of light?

A

diffraction grating
creates bright central line called zero order
and other maxima and minima are first, second orders etc.

physics content ocr a (4 decks)

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