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A level physics > Waves > Flashcards

Waves Flashcards

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1
Q

What are mechanical waves?

A

Waves that require a medium to travel through

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2
Q

Give examples of mechanical waves

A

Sound waves

Seismic waves

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3
Q

What are electromagnetic waves?

A

Oscillating electric and magnetic fields that travel without the need of a medium

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4
Q

Give an example of electromagnetic waves

A

All electromagnetic waves

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5
Q

What are longitudinal waves?

A

Waves, whose direction of vibration is parallel to the direction of wave travel

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6
Q

Give examples of longitudinal waves?

A

Sound

Primary seismic waves

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7
Q

What are transverse waves?

A

Waves, whose direction of vibration is perpendicular to the direction of wave travel

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8
Q

Give examples of transverse waves

A

All electromagnetic waves

Secondary seismic waves

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9
Q

What is the amplitude?

A

The length from the trough/crest to the equilibrium, maximum displacement

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10
Q

What is the wavelength?

A

The distance in metres between the same point on two successive waves

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11
Q

What is frequency?

A

The number of cycles per second(Hz)

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12
Q

What is displacement?

A

The distance of a vibrating particle from its equilibrium position

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13
Q

What is a cycle?

A

The maximum displacement from one wave to the next

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14
Q

What is the time period?

A

The time for one complete wave to pass a fixed point

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15
Q

What is the equation for the time period?

A

T = 1/f

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16
Q

What happens to the wavelength when the frequency of a wave increases?

A

The wavelength shortens when the frequency increases

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17
Q

What is the equation for wave-speed?

A

Wave-speed = frequency * wavelength

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18
Q

What is polarisation?

A

The production of waves oscillating in one plane from a source of randomly oscillating waves

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19
Q

What does it mean when the waves are unpolarised?

A

Waves are unpolarised when the vibrations change from one plane to another

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20
Q

What happens when a light goes through a polaroid?

A

The light travelling through the polaroid has a reduced intensity as it is polarised due to the arrangements of the molecules in the polaroid

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21
Q

What is reflection?

A

The wave is bounced back when it hits a boundary

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22
Q

What is refraction?

A

The wave changed direction as it enters a different medium

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23
Q

What is the constant speed of all EM waves in a vacuum?

A

3.00*10^8m/s

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24
Q

How do X-rays and Gamma rays cause ionisation?

A

They knock electrons out of orbits

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25
Q

What is a progressive wave?

A

A wave that caries energy from one place to another without transferring any material

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26
Q

What evidence shows that electromagnetic waves are transverse?

A

Polarisation

In 1808, Etienne Louis Malus discovered that light was polarised by reflection

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27
Q

Why can light be polarised?

A

Light is a transverse wave consisting of vibrating electric and magnetic fields at right angles to the transfer of energy

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28
Q

When does superposition happen?

A

When two or more waves pass through each other

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29
Q

What is the principle of superposition?

A

When two or more waves cross and the resultant displacement equals the vector sum of the individual displacements

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30
Q

How can interference be described?

A

Constructive or destuctive

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31
Q

Give two examples of when constructive interference can occur

A

Crest + Crest = Supercrest

Trough + Trough = Supertrough

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32
Q

Give an example of destructive interference

A

Crest + Trough = Zero

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33
Q

What does it mean when waves are in phase?

A

The wave meet at the same point in the wave cycle

At the point, they have the same displacement and velocity

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34
Q

What is 360 in radians?

A

2Pi radians

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35
Q

How do you convert from degrees to radians and vice versa?

A

Degrees to radians, multiply by Pi/180

Radians to degrees, multiply by 180/Pi

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36
Q

What does it mean if sources are coherent?

A

The coherent sources have the same wavelength and frequency and a fixed phase difference between them

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37
Q

What factor affects interference?

A

Path difference

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38
Q

What is the path difference?

A

The amount by which the path travelled by one wave is longer than the path travelled by the other wave

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39
Q

When does constructive interference occur?

A

When there is an equal distance at a point from two sources that are coherent and in phase
Also when the path difference is a whole number of wavelengths
Path difference = n(wavelengths)

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40
Q

When does destructive interference occur?

A

The path difference is half a wavelength or one and a half e.t.c wavelengths out of phase
path difference = (n+0.5)wavelengths

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41
Q

What is diffraction?

A

The spreading out of waves as they go through a narrow gap or go around obstacles

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42
Q

What factors affect diffraction?

A

Wavelength

Size of the gap

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43
Q

When is the diffraction unnoticeable?

A

The size of the gap is bigger than the wavelength

44
Q

When does most diffraction occur?

A

The size of the gap is the same as the wavelength

45
Q

When are most of the waves reflected back?

A

The size of the gap is smaller than the wavelength

46
Q

What is needed to observe a clear diffraction pattern?

A

A monochromatic, coherent light source

47
Q

Give an example of a monochromatic and coherent light source

A

Lasers

48
Q

What is the meaning of monochromatic?

A

All the light has the same wavelength, frequency, and therefore the same colour

49
Q

What can be observed when a monochromatic, coherent laser light is shone through a narrow list?

A

A central bright fringe with dark and bright fringes alternating on either side

50
Q

What type of interference causes the dark fringes?

A

Destructive interference

51
Q

What type of interference causes the bright fringes?

A

Constructive interference

52
Q

What is white light?

A

A mixture of difference colours, each with different wavelengths

53
Q

What happens when white light is shone through a single narrow slit?

A

All the different wavelengths are diffracted by different amounts
You get a spectra of colours rather than clear fringes

54
Q

What is the intensity of light?

A

The power per unit area

55
Q

Why is the central maximum in a single slit light diffraction the brightest?

A

There are more photons per unit area hitting the central maximum per second than the other bright fringes

56
Q

What factors affect the width of the central maximum?

A

Wavelength

Slit size

57
Q

What happens when the slit width is increased?

A

The amount of diffraction decreases
The central maximum is narrower
The intensity of the central maximum is higher

58
Q

What happens when the wavelength is increased?

A

The amount of diffraction increases
The central maximum is wider
The intensity of the central maximum is lower

59
Q

What can you do to prevent damage when using lasers?

A 
Never shine the laser towards a person
Wear laser safety goggles
Avoid shining the laser beam at a reflective source
Have a warning sign on display
Turn the laser off when it's not needed
60
Q

Describe the Young’s Double Slit experiment?

A

A laser is shone through two slits onto a screen
The slits have to be about the same size as the wavelength so that the laser light is diffracted
You get a pattern of light and dark fringes

61
Q

Describe a similar experiment to the Young’s slit experiment with microwaves

A

Replace the laser and slits with two microwave transmitter cones attached to the same signal generator
Replace the screen with a microwave receiver probe
If you move the probe perpendicular to the microwave generator, you’ll get an alternating pattern of strong and weak signals

62
Q

What is the Young’s Slit formula?

A

w=(wavelength*D)/s

63
Q

What is the meaning of fringe spacing?`

A

The distance between the centre of the one minimum to the centre of the next minimum or the centre from one maximum to the centre of the next maximum

64
Q

What is ‘s’ in Young’s slit formula?

A

Spacing between slits

65
Q

What is ‘D’ in Young’ slit formula?

A

The distance from the slits to the screen

66
Q

What was Young’s slit experiment evidence for?

A

It showed that light could both diffract and interfere

67
Q

What happens when light diffracts through more slits?

A

Interference patterns become sharper

68
Q

Which order is the maximum brightness?

A

Zero-order

69
Q

How can the wavelength be calculated from diffraction grating?

A

wavelength = d*sin(angle)/n

70
Q

How would you calculate the slit spacing(d), if you are given the number of slits per metre?

A

d = 1/slits per metre

71
Q

What general conclusions can be drawn from dsin(angle) = nwavelength?

A

If the wavelength is bigger, the bigger the angle.
If d is bigger, the smaller the angle.
Values of sin(angle) greater than 1 means the order doesn’t exist

72
Q

How can diffraction grating be used?

A

It can be used to identify elements

It can be used to calculate atomic spacing

73
Q

What is white light?

A

A mixture of colours with different wavelengths

74
Q

What will happen if you diffract white light?

A

The colours in the light will spread out by different amounts because of the different wavelengths

75
Q

Which colour will be on the inside and on the outside?

Why?

A 
Inside = violet, has the shortest wavelength
Outside = red, has the longest wavelength
76
Q

What is a stationary wave?

A

The superposition of two progressive waves with the same frequency and wavelength moving in opposite directions

77
Q

What don’t stationary waves transmit?

A

Stationary waves do not transmit energy

78
Q

What is a node?

A

This is where the amplitude of the vibration is zero

79
Q

What is an antinode?

A

This is where the point of maximum amplitude

80
Q

Where do stationary waves occur?

A

They occur at certain special values of frequency and wavelength called harmonics

81
Q

What causes progressive and stationary waves?

A

Fluctuation

Disturbance

82
Q

What is the difference in energy transfer between stationary and progressive waves?

A

Progressive waves
-transfer energy and momentum from the source to
surroundings
Stationary waves
-no energy or momentum transfer as they are confined
to a specific region

83
Q

What is the difference in occurrences between stationary and progressive waves?

A

Progressive waves
-occur at all frequencies
Stationary waves
-occur at harmonics

84
Q

What is the difference in the amplitude of particles between stationary and progressive waves?

A

Progressive waves
-all particles will reach a maximum and minimum
amplitude
Stationary waves
-some points have a maximum amplitude and others
do not. The amplitude of the particle depends on the
position of the particle

85
Q

What is the difference in the phase difference of particles between stationary and progressive waves?

A

Progressive waves
-only particles exactly one wavelength apart move in
phase with each other
Stationary waves
-within a one-half wavelength, all particles move in
phase

86
Q

What is the first harmonic on a string?

A

Length = wavelength/2

87
Q

What is the second harmonic on a string?

A

Length = wavelength

88
Q

What is the general formula for the length of the string?

A

Length = n*wavelength / 2

89
Q

Wha is the first harmonic in a tube with one closed end?

A

Length = wavelength/4

90
Q

What is the second harmonic in a tube with one closed end?

A

Length = 3/4 * wavelength

91
Q

What is the first harmonic in a tube with both ends open?

A

Length = wavelength/2

92
Q

What is the second harmonic in a tube with both ends open?

A

Length = wavelength

93
Q

What is the fundamental mode frequency?

A

f = 1/2L√(T/µ)

94
Q

What is the second harmonic frequency?

A

f = 1/L√(T/µ)

95
Q

What is the third harmonic frequency?

A

f = 3/2L√(T/µ)

96
Q

What is refraction?

A

The change in direction that occurs when light passes at an angle across a boundary between 2 transparent substances

97
Q

What happens to the light when it travels from a less dense material to a more dense material?

A

The light bends towards the normal

98
Q

What happens to the light when it travels from a more dense material to a less dense material?

A

The light bends away from the normal

99
Q

What is the refractive index of a material?

A

It is a measure of how much the material slows down light

100
Q

What is the absolute refractive index of a material?

A

A measure of optical density

it is found from the ratio between the speed of light in a vacuum and the speed of light in that material

101
Q

How do you calculate the refractive index of a substance?

A

n = C/Cs

102
Q

What is the relative refractive index between two materials?

A

The ratio of the speed of light in material 1 to the speed of light in material 2

103
Q

How do you calculate the relative refractive index?

A

n = C1/C2

104
Q

What is the refractive index of air?

A

1

105
Q

What is the angle of incidence?

A

The angle the incoming light makes to the normal

106
Q

What is the angle of refraction?

A

The angle the refracted ray makes to the normal

107
Q

What is Snell’s law?

A

n1 sin angle 1 = n2 sin angle2

A level physics (15 decks)

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