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LC Physics > Light as a wave + Waves&WaveMotion > Flashcards

Light as a wave + Waves&WaveMotion Flashcards

1
Q

Spectrometer

A

Used to study light (as a wave)

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2
Q

What spectrometer consists of

A

Collimator (c)
Telescope (t)
Circular scale
Rotating table

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3
Q

Collimator

A

Tube with a slit (s) at one end and a converging lens at other

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4
Q

Telescope

A

With corsswires in the eyepiece

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5
Q

Circular scale

A

Marked in degrees with vernier scales attached

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6
Q

Rotating table

A

With three levelling screws

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7
Q

Spectrometer set up

A
  1. Adjust eyepiece until crosswires can be seen clearly
  2. Focus the telescope on a distant object
  3. Place a lamp in front of the slit, place telescope in line with collimator
  4. Adjust slit to give narrow beam of light
  5. Adjust telescope until image of slit coincides with crosswires without parallax
  6. Level the table
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8
Q

Camera

A
  1. Mimics how eye works
  2. Lens can be moved in/out
  3. Amount of light entering camera
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9
Q

Prism

A
  • Using a prism, Isaac Newton found that white light can be split up into its spectrum of colours through a process called dispersion
  • It is split up into seven colours: roygbiv
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10
Q

Dispersion

A

the splitting up of white lgiht into its constituent colours

/ separation of light into its diff colours/frequencies/wavelengths

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11
Q

Dispersion - why it happens

A

They split up like this because different colours have different wavelengths, as light travels through different media long wavelengths are refreacted least, short wavelengths are refracted more

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12
Q

Primary colours

A

Red, green, blue

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13
Q

Secondary colours

A

Combinations of primary colours

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14
Q

Complementary colours

A

A primary colour + a secondary colour which together give white (eg. blue and yellow)

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15
Q

Dispersion by a grating

A
  • Light is diffracted + dispersed when it goes through a grating
  • Red light is deviated the most (longest wavelength), violet the least (shortest wavelength)
  • No overlap of the spectrum occurs when using a grating
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16
Q

The diffraction grating

A

Square of plastic with slits in it

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17
Q

Distance formula for diffraction grating

A

d = 1/600 mm

d= 1/600 / 1000 m (metres)

the 600 is how many lines per mm, eg. can be 400 or 500, etc

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18
Q

Diffraction grating equation

A

nλ = d sinΘ

n = number of images
λ = wavelength (lambda)
d = diffraction of grating constant
Θ = angle (theta)
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19
Q

max number of images to one side of grating

equation (highest order image formula)

A

nₘₐₓ = d/λ

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20
Q

Infra-red applications

A
  1. Used to heal damaged muscle
  2. To take thermographs of the body
  3. Remote controls for TV + Radio
  4. Burgular alarms
  5. Fire-fighters use IR viewers to find unconscious people
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21
Q

Ultraviolet

A

Given off by the sun, helps to produce Vit. D can cause sunburn + cancer

Ozones layer absorbs most of UV radiation

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22
Q

Ultraviolet application

A
  1. UV lightbulbs
  2. Washing powders
  3. Security pens
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23
Q

Microwaves

A

Radio waves of short wavelenghts

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24
Q

Microwaves application

A
  1. Communication - travel in straight lines from transmitter to receiver within 40 miles of each other
  2. Cooking - microwaes are reflected by metal but absorbed by water, sugar and fat
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25
Q

Fraunhofer lines

A

Emission spectrum

Absorption spectrum

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26
Q

Emission Spectrum

A

A spectrum given out by a substance when its atoms are excited

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27
Q

Absorption Spectrum

A

.A spectrum that is continuous except for certain missing wavelengths (absorbed by gases) (first measured by German Joseph von Fraunhofer)

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28
Q

Types of colours

A

primary colours
secondary colours
complementary colours

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29
Q

Grating constant

A

The distance (d) between two adjacent slits on thegrating is called the Grating Constant

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30
Q

Lines in diffraction grating

A

has 400/500/600 lines per mm usually

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31
Q

Infra-red

A

Given off by warm objects

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32
Q

What does LASER stand for

A

Light Amplification by Stimulated Emission of Radiation

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33
Q

What does a laser tube do

A

A laser tube produces a beam of light in which all the waves are of the same frequency and in phase

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34
Q

Application of lasers

A
  1. Used to treat detached retina
  2. Used in surgery
  3. Used to cut clothing + metal
  4. Used to read CDs
  5. Used to scan things in shops
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35
Q

Polarisation

A
  • Light from incandescent source is unpolarised
  • If light from source is passed thru substance called Polaroid, becomes plane polarised. (light is vibrating in one place only)
  • If second Polaroid is rotated thru 90 degrees, virtually no light gets thru. Since only transverse waves can be polarised, the fact that light can be polarised shows light is a transverse wave.
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36
Q

Stress polarisation

A

This phenomenon is called photoelasticity + it’s used by engineers to analyse stresses in components

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37
Q

Light that passes through the diffraction grating makes an angle theta with the normal to the grating

A
  1. Parallel rays of monochromatic light of wavelength λ are incident on diffraction grating in which slit separation is d. If grating has N lines per metre, grating spacing is given by: d = 1/N metres
  2. Constructive interference only occurs along a few precise directions, like when PQ = λ and when other whole number wavelengths exist PQ = nλ where n = 0,1,2,3…
  3. Now: PQ = dsinθ where θ is angle of diffraction
    Therefore nλ = dsinθ
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38
Q

Plural of medium

A

Media

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39
Q

Three possible states of substances

A

Substances can exist in three possible states:

Solid
Liquid
Gas

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40
Q

Waves and medium

A

When a wave passes through a solid/liquid/gas. we say it passes through a medium.
If it doesn’t, it does not need a medium.

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41
Q

Categories of waves

A

Mechanical

Electromagnetic

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42
Q

Mechanical

A

Waves that need a medium are called mechanical.
They travel through vibrations of molecules.

eg. water wave, waves on rope/spring, sound waves, ultrasonic waves

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43
Q

Electromagnetic

A

Waves that do not need a medium are called electromagnetic.
They travel at the speed of light

eg. radio waves, microwaves, infra-red waves, light waves, x-rays

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44
Q

Travelling wave

A

A travelling waves carries energy from the source to another place.
Can be either mechanical or electromagnetic

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45
Q

Periodic travelling wave

A

If the wave travels in a controlled pattern, it is called a periodic travelling wave, because the thing is controlled

46
Q

Travelling waves - slinky

A
  • When we look at a Slinky, energy can pass along its length.
  • If some coils are pulled together we call this compression
  • When compression is let go it travels along length
  • Region left behind stretches more than normal and this is called rarefaction
47
Q

Waves - groups

A

Waves can be further divided into groups depending on how they vibrate:
Transverse
Longitudinal

48
Q

Transverse

A
  • Waves that vibrate up + down
  • vibrations perpendicular to direction of propagation of wave
  • Only transverse waves can be polarised
49
Q

Longitudinal

A
  • Waves that vibrate lengthways

- vibrations parallel to direction of propagation of wave

50
Q

Eg of transverse waves

A

waves on a rope/string (not compression), water waves, all electromagnetic waves

51
Q

Eg of longitudinal waves

A

compressions on a spring, sound waves in a medium, ultrasonic waves

52
Q

Frequency

A

Frequency of a wave means how often one fullw ave, or cycle, passes a point

53
Q

Frequency unit + symbol

A

Unit: the Hertz (Hz)
1 hertz = 1 cycle per second

Symbol: f

54
Q

Amplitude

A
  • When particles are at rest, the position they are in is the starting or resting position
  • When they are vibrating due to energy being introduced they reach their amplitude, or height

The amplitude of a wave is its height

55
Q

Starting/resting position

A

When the particles are at rest, the position they are in is the starting or resting position

56
Q

Wavelength

A

The length of a wave, or wavelength, in the distance from one point on one wave to the same point on the next wave

-distance between two crests/troughs

57
Q

Wavelength unit + symbol

A

Unit of wavelength: metre

Symbol: λ (lambda)

58
Q

Velocity

A

The distance travelled by one cycle in one second is the velocity of the wave

59
Q

Velocity unit + symbol

A

Unit: metre per second

Symbol: c

60
Q

Finding c

A

We can work out the velocity of a wave by multiplying the frequency and the wavelength

c = fλ

61
Q

C unit

A

metre per second

62
Q

Phenomenon

A

An observable occurence

63
Q

Wave phenomena

A 
Reflection
Echo
Refraction
Diffraction
Interference
64
Q

Reflection

A

The bouncing of waves off an obstacle in their path

eg. water waves, light waves, waves on a slinky

65
Q

Echo

A

A sound wave reflected off something

66
Q

Wave speed

A
  • When waves move from one medium to another, frequency stays the same
  • Wavelength increases if waves speed up
  • Wavelength decreases if waves slow down
67
Q

Refraction

A

When wave enters new medium + changes velocity, its direction changes (called refraction)

eg. water waves in a ripple tank

68
Q

Diffraction

A

The spreading of waves into a region beyond an obstacle or gap

eg. water waves in a ripple tank, sound waves, electromagnetic waves, light waves

69
Q

Interference

A
  • When two waves meet, they form a new wave
  • This new ave has an amplitude that depends on the values of the amplitudes of the two original waves
  • Interference can be constructive or destructive

-when waves from different sources overlap, a new wave is formed

70
Q

Interference types

A

Constructive

Destructive

71
Q

Constructive

A

Constructive interference happens when the resulting amplitude is greater than the amplitudes of the individual waves

72
Q

Destructive

A

Destructive interference happens when the resulting amplitude is less than the amplitude of the individual waves

73
Q

Coherent source

A

When two waves are in phase with each other, or there is a constant phase change. They have the same frequency

74
Q

Interference pattern

A

When two or more coherent waves meet, they make a wave pattern called an interference pattern

75
Q

Polarisation

A

Means controlling the vibrations of a wave so it vibrates in one plane only
Only transverse waves can be polarised

76
Q

Vertically polarised

A

Polarisation is also called vertically polarised

77
Q

Plane of polarisation

A

The plane through which it travels

78
Q

finding wavelength

A

when using formula in exam, make sure to find average wavelength of all angles

79
Q

finding N max

A

find using formula, which gives max no. of images to one side. Twice this number and add 1 to find N max.

ie. (Max images to one side + Max images to other side + central image)

80
Q

photocell

A

know how to draw diagram

81
Q

describe how a photocell conducts current

A
  • light of suitable freq falls on cathode

- electrons are emitted

82
Q

a current of 2 microA is flowing in a photocell. How many electrons are generated in the photocell during each minut?

A

use Q = It

then use it with electron charge to find no. of electrons

83
Q

diffraction effects of sound waves are noticeable in everyday life, whereas the diffraction effects of light are not. Explain why

A
  • sound has a long wavelength. Noticeable in everyday life etc. sound diffracted as it goes through a window
  • Light has a short wavelength. Need a diffraction grating/very small gap
84
Q

light dispersed with a prism order of colours starting with colour refracted the least

A

red orange yellow green blue indigo violet

85
Q

in Young’s experiment to demonstrate the wave nature of light he needed two coherent sources of light. How might he have produced these sources?

A

double slits

86
Q

calculate the energy of a photon of green light

A

c = fλ

E = hf

87
Q

Quantum mechanics is used to explain how electrons in atoms produce line emission spectra. Describe how these spectra are produced.

A
  • electrons gain energy energy to move to a higher energy level
  • return (to lower energy level) emitting photon/light/em radiation
88
Q

two differences between photons and electrons

A
  • photons have no mass
  • photons have no charge
  • photons are light/electromagnetic radiation
  • photons are packets/bundles of energy
89
Q

properties of radio waves

A
  • travel at speed of light
  • electromagnetic radiation
  • travel thru vacuum
90
Q

SAR value (specific absorption rate)

A

SAR = W/kg

91
Q

what happens to radio freq energy absorbed by body

A

converted to heat

+ carried away by body

92
Q

why are radio freq waves not very penetrating

A

low freq / long wavelength / low energy

93
Q

what are the audible freq limits for sound waves?

A

Lower value ≈ 20 Hz

Upper value ≈ 20,000 Hz

94
Q

safety precautions to take when using a mobile phone

A

keep phone at distance
use loudspeaker function
brief calls only
direct antenna away from your head

95
Q

an electromagnetic wave which may induce cancer + how

A

x-rays
UV rays

cause ionisation of body cells

96
Q

properties common to all types of electromagnetic waves

A
  • same speed
  • can be polarised/reflected/diffracted etc
  • travel through vacuum
97
Q

energy of a photon

A

E = hf

c = fλ

98
Q

diffraction grating experiment - observation if laser was replaced with white light

A

spectra / dispersion / colours

99
Q

Observation when a narrow beam of light undergoes dispersion as it passes through a prism

A
  • red light deviated least

- only one spectrum observed

100
Q

Observation when a narrow beam of light undergoes dispersion as it passes through a diffraction grating

A
  • red light deviated most

- many spectra observed with a grating

101
Q

example of light undergoing dispersion besides prism + grating

A

rainbow

102
Q

what causes a vapour lamp to emit light

A

electrons changing energy levels

103
Q

How to detect infra red

A
  • thermometer
  • temperature sensor
  • photographic plate
104
Q

How to detect ultra violet

A
  • shine on vaseline/detergents
  • effect eg. fluorescence
  • glows
105
Q

An electromagnetic radiation has a wavelength of x metres, name the section of the spectrum in which this radiation is located

A
  • find its freq using c=fλ

- know freqs of each section

106
Q

Can a diffraction grating diffract x-rays? why?

A

no,

  • line spacing must be similar to wavelength of radiation (for diffraction to occur)
  • spacing between lines in a grating is too large
107
Q

differences between longitudinal and transverse waves

A
  • transverse can be polarise, longitudinal cannot

- state way they travel

108
Q

why is a fluorescent tube an efficient source of light?

A

-most of the electrical energy is converted to light energy

109
Q

why does diffraction not occur when light passes through a window?

A

width of window is too large

110
Q

how does the diffraction grating produce a spectrum

A

diff colours have diff wavelengths/frequencies

constructive interference occurs / bright images formed at different Θ

111
Q

why is a spectrum not formed at the central (zero order) image

A

at central image, Θ = 0

LC Physics (25 decks)

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