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Physics > Waves, EM Spectrum and Radiation > Flashcards

Waves, EM Spectrum and Radiation Flashcards

1
Q

Amplitude of a wave

A

Displacement from rest position to trough / crest

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2
Q

Wave length in a wave

A

Length of a full cycle of one wave

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3
Q

Frequency of a wave

A

Number of complete cycles of a wave per second

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4
Q

Period of a wave

A

How long it takes to make a full cycle

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5
Q

Transverse wave definition

A

Waves with vibrations perpendicular to the direction of travel e.g. EM waves, S-waves, waves in water

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6
Q

Longitudinal wave definition

A

Waves with vibrations parallel to the direction of travel e.g. sound waves, P-waves

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7
Q

Wave speed formula

A

Wave speed = frequency x wavelength

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8
Q

How to measure speed of sound

A
  • set up oscilloscope so detected waves at each microphone are shown as separate waves
  • start with both microphones at the speaker, then slowly move one away until both waves are aligned
  • measure distance between both microphones to find one wavelength
  • multiply this by frequency of signal generator attached to speaker
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9
Q

Transmission of waves through second material

A

Wave carries in travelling through second material

Normally leads to refraction

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10
Q

Reflection of waves

A

Wave is sent back away from the second material

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11
Q

Wave is absorbed by second material

A

Wave transfers energy to material’s energy store e.g. transferred to thermal energy like in a microwave

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12
Q

Refraction

A

When waves change direction when entering a material of different density at an angle

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13
Q

What happens to the wave when the second medium is denser?

A

Bends towards the normal as it slows down

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14
Q

What happens to the wave when the second medium is less dense?

A

Bends away from the medium and speeds up

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15
Q

The shorter the wavelength of an EM wave..

A

The more it will bend

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16
Q

What are sound waves and what causes them?

A

Longitudinal waves

Series of compression and rare fractions caused by vibrating objects

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17
Q

Factors affecting what frequencies of sound can transfer through an object

A

Object size
Object shape
Object structure

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18
Q

Order of which medium sound travels in fastest (fastest to slowest)

A

Solid
Liquid
Gas

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19
Q

Why can’t we detect the refraction of sound waves?

A

Sound waves spread out so much that we cannot see the change in direction

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20
Q

Why can’t sound travel in vacuums?

A

There are no particles that vibrate to allow sound to travel

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21
Q

What happens when sound tries to travel through flat, hard surfaces?

A

They will be reflected and cause echoes

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22
Q

How we hear sounds method

A
  • sound waves reach eardrum and it vibrates
  • the vibrations pass on to ossicles, through semicircular canals and to cochlea
  • cochlea turns vibrations into electrical signals sent to the brain
  • brain interprets signals as sounds of different pitches and volumes depending on frequency and intensity
  • higher pitches = higher frequency
  • range of sounds we can hear depends on the shape of parts of the ear
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23
Q

Definition of ultrasound

A

Sound with frequencies over 20,000 Hz

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24
Q

How are ultrasounds generated?

A

Electrical devices generate electrical oscillations of any frequencies and are converted and produced by mechanical vibrations

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25
Q

Uses of ultrasound

A

Medical imaging
Industrial imaging
Echo sounding

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26
Q

How does medical imaging work?

A
  • Ultrasound waves pass through body but is reflected or refracted when passing through 2 different mediums
  • the exact timing and distribution of the echoes are processed by computer to produce a video image
  • it is completely safe
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27
Q

How does industrial imaging work?

A
  • ultrasound waves entering a material will be reflected back by the far side of the material
  • if they are reflected back sooner, a flaw is present and can be found
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28
Q

How does echo-sounding work?

A
  • ultrasound will always be reflected back

- the time it takes to come back can be used to calculate distance from objects or the sea bed

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29
Q

Infrasound definition

A

Sound with frequencies lower than 20Hz

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30
Q

Uses of infrasound

A

Communication between animals e.g. whales
Produced by natural events e.g. earthquakes so they can be predicted
Exploring the structure of the Earth

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31
Q

P-waves facts

A

Longitudinal
Can travel through solids and liquids
Faster than S-waves

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32
Q

S-waves facts

A

Transverse
Only travel through solids
Slower than P-waves

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33
Q

How to calculate angle of reflection

A

Angle of reflection = angle of incidence (angle bateen incident ray and the normal)

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34
Q

Speculate reflection definition

A

When light is reflected on a flat, smooth surface

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35
Q

Diffuse reflection definition

A

When light is reflected on a touch surface so waves are reflected on all kinds of directions

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36
Q

Why are objects white?

A

They reflect back all wavelength of visible light equally

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37
Q

Why are objects black?

A

They absorb all wavelengths of visible light

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38
Q

Why are objects translucent or transparent?

A

They transmit some, most or all and the light passes through them

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39
Q

Why are objects certain colours?

A

They absorb all other wavelengths of light except one, which they reflect

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40
Q

How do colour filters work?

A
  • white light is shone through them
  • primary colour filters absorb all wavelengths of the light apart from one colour (e.g. blue)
  • secondary colour filters transmit the wavelengths corresponding to its colour
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41
Q

EM waves facts

A

Transverse
All travel at same speed in vacuums but different speeds in different materials

Grouped into seven basic types but all on a spectrum

Generated by changes in atoms and their nuclei

All transfer energy from source to absorber

The higher the frequency, the more energy it has

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42
Q

7 parts of the EM spectrum

A 
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
43
Q

Effect of radio waves on human health

A

-radio waves pass through the body

44
Q

Effect of microwaves on human health

A

Some can be absorbed, heating cells and can be dangerous

45
Q

Effect of infrared on human health

A

Mostly reflected or absorbed by skin, causing some heating and can cause burns when too hot

46
Q

Effect of ultraviolet on human health

A

Absorbed by skin
Ionising
Can cause skin cancer, eye conditions and blindness

47
Q

Effect of X-rays and gamma rays on human health

A

Highest frequencies, so more energy and more damage can be caused
Passes through skin so deeper tissues are affected

48
Q

What are colour is the best emitter of radiation?

A

Black

49
Q

How are radio waves generated?

A
  • alternating current in a circuit has electrons that oscillate to create radio waves
  • radio wave has same frequency as electric current that made it
50
Q

Uses of radio waves

A
  • long-wave radio can be bend so can be received halfway round the Earth
  • short-wave radio are reflected by Earth’s atmosphere so can be received around the Earth
  • Bluetooth uses short-wave radio to send data over short distances without wires
  • radio waves used for TV and FM are very short so you must have direct sight or transmitter
51
Q

Microwaves and radio waves in satellites

A

microwave or radio wave signal from transmitter on Earth is sent to satellite in space. It then sends the signal back to a different direction to Earth so another satellite dish picks it up

52
Q

Uses of microwaves

A
  • communications (satellites)
  • microwave ovens transmit microwaves onto food containing water molecules
  • the water molecules absorb the transferred heat energy and spreads this heat to the rest of the food
53
Q

Uses of infrared

A
  • Infrared cameras
  • thermal imaging
  • infrared sensors
  • electric heaters
  • optic fibres
  • TV remotes
54
Q

Uses of visible light

A
  • seeing

- photography

55
Q

Uses of UV

A
  • fluorescent lights
  • security pens
  • banknotes and passports
  • sterilisation of water (kills bacteria)
56
Q

Uses of X-rays

A
  • X-ray images
  • medical imagery
  • security
57
Q

Uses of gamma rays

A
  • sterilising food and equipment
  • medical imaging (PET scans)
  • cancer treatment
58
Q

How does movement of electrons generate radiation?

A
  • electron absorbs right amount of energy
  • it gets “excited” and moves up a higher energy shell
  • it will go back down to its original shell but emits the same amount of energy it absorbed as radiation
  • what radiation is emitted depends on energy levels it moves between
  • movement between second and third level is lower than movement between first and second level
59
Q

How does an atom lose electrons?

A

It absorbs enough energy that it moves so far that it leaves the atom
This makes the atom an ion and has been ionised

60
Q

Ionising radiation definition

A

Any radiation that can knock off electrons from atoms

61
Q

Isotope definition

A

Same element of an atom that has a different mass number

62
Q

What is mass number?

A

Amount of protons and neutrons

63
Q

What is atomic number?

A

Amount of protons

64
Q

Isotope facts

A

Usually less stable than elements
Tend to decay and emit radiation
Elements usually only have 1 or 2 stable isotopes

65
Q

What are alpha particles?

A

Helium nuclei

66
Q

What is alpha radiation?

A

When an alpha particle is emitted from the nucleus

67
Q

Alpha particles facts

A 
Low penetration (stopped by few cm of air, sheet of paper)
Strongly ionising (due to size)
68
Q

What are beta particles?

A

Fast-moving electrons / positrons

69
Q

What is beta radiation?

A

When beta particles are emitted by the nucleus.

70
Q

Beta particles facts

A 
Moderate penetration (stopped by few metres of air, 5mm of aluminium)
Moderate ionisation
71
Q

What is gamma radiation?

A

Radiation emitted from the nucleus due to nuclear rearrangement

72
Q

Gamma radiation facts

A 
High penetration (stopped by thick sheets of lead, metres of concrete)
Weakly ionising
73
Q

What happens in beta-minus decay?

A

Neutron changes into a proton and electron

Electron gets emitted and proton stays

74
Q

What happens in positron emission?

A

A proton changes into a neutron and positron

Positron is emitted and neutron stays

75
Q

What happens in neutron emission?

A

A neutron gets emitted

76
Q

Why can’t you predict when an isotope will decay?

A

Radioactivity is random

77
Q

What is activity measured in?

A

becquerels (Bq)

78
Q

Definition of half-life

A

Average time taken for number of radioactive nuclei in an isotope to halve

79
Q

How to find half-life on a graph

A

Time taken for activity to halve

80
Q

Background radiation definition

A

Low-level radiation that’s around us all the time

81
Q

Background radiation examples

A
  • naturally occurring unstable isotopes e.g. in the air, rocks, building areas
  • radiation from space e.g. from the Sun
  • radiation from human activities e.g. fallout from nuclear explosions, nuclear waste
82
Q

Irradiation definition

A

Exposure to radiation

83
Q

How to prevent irradiation?

A
  • keeping sources in lead-lined boxes
  • using remote-controlled arms from a different room when handling radioactive sources
  • wearing photographic film badges to monitor exposure
84
Q

Contamination definition

A

Radioactive particles getting onto objects

85
Q

How to prevent contamination?

A
  • wearing gloves and using tongs when handling radioactive substances
  • wearing protective suits to prevent them from breathing particles in
86
Q

How does radiation damage cells?

A
  • ionising radiation enters living cells and ionises molecules within them
  • lower doses causes minor damage without killing cells. Damaged DNA may lead to cancer
  • higher doses kill cells completely, leading to vomiting, hair loss and tiredness
  • gamma and beta are most dangerous outside of the body as they can penetrate the skin and damage delicate organs
  • alpha is most dangerous inside the body as it is highly ionising and cause the most damage
87
Q

Uses of alpha radiation

A

smoke detector:

  • weak source of alpha radiation, close to two electrodes
  • source causes ionisation and current of charged particles flow
  • if fire is present, smoke will absorb charged particles, causing current to stop and alarm sounds
88
Q

Uses of gramma radiation

A
  • sterilisation of food

- sterilisation of medical equipment

89
Q

Uses of radioactive tracers

A

medical imagery:

  • patient ingests / is injected tracers (beta or gamma radiation)
  • isotope emits radiation and this can be detected by external detectors e.g. PET scans

underground leaks:

  • isotope is inserted into pipes
  • isotope decays and releases gamma radiation
  • radiation shouldn’t be detected due to lead pipes so if detected, cracks are present
90
Q

Radiation in thickness gauge

A
  • paper is rolled on a conveyor belt
  • a beta source emits beta radiation continuously and passes through the paper and towards a detector beneath it
  • if the detector doesn’t detect beta radiation, it is because the paper is too thick and the beta particles cannot pass through
  • if so, the rollers adjusted until the detector senses beta radiation again
91
Q

PET scan method

A
  • inject patient with tracer (substance present in the body, short half-life)
  • positron from emitted from tracer meets with electron from an organ and annihilate, emitting gamma radiation
  • cells with higher metabolism (e.g. cancer cells) have more tracer so more radiation is detected at that point
  • detectors around the body detect this radiation and a computer created an image showing concentration of radiotracer
92
Q

Alpha radiation in treating tumours

A

Alpha emitters injected near the tumour

Lots of damage done to nearby area (cancer cells) but damage to healthy cells is limited due to short range

93
Q

Beta radiation in treating tumours

A

Beta emitter is implanted nearby or in tumour
Beta radiation can pass through casing of implant before damaging cancerous cells
Can damage healthy cells further away

94
Q

Gamma radiation in treating tumours

A

Gamma rays carefully aimed at tumour as they are able to penetrate through patient’s body
Shielding is sometimes used but some damage will still be done to healthy cells

95
Q

Definition of nuclear fission

A

The splitting up of large atomic nuclei

96
Q

Chain reaction in nuclear fission method

A
  • slow-moving neutron is fried at a large, unstable nucleus
  • this makes the nucleus more unstable and it becomes more unstable
  • this makes two daughter nuclei and energy is released
  • two or three more neutrons are also spat out, causing other nuclei to split up and so on
97
Q

How to control chain reactions

A
  • uranium fuel rods are kept in a moderator to slow down fast-moving neutrons
  • control rods (usually boron), limit the rate of fission by absorbing excess neutrons
  • we aim to make one new neutron per fission
98
Q

How do we generate energy from fission?

A
  • thermal energy is released from fission
  • cool water is pumped through to the boiler where it meets the thermal energy
  • this heats it up and steam is created, which pushes a turbine attached to an electric generator
99
Q

Nuclear fusion definition

A

When two light nuclei collide to make a larger heavier nucleus
The mass of the heavier nucleus doesn’t have as much mass as the two lighter nuclei as some is converted to energy

100
Q

Conditions for nuclear fusion and why

A

Very high pressures
Very high temperatures
As to overcome the electrostatic forces of repulsion between 2 positively-charged nuclei (they need to be close to fuse)

101
Q

Advantages of nuclear power

A

Pretty safe way of generating electricity
Very reliable energy resource
No products that lead to global warming and acid rain
Huge amounts of energy produced from relatively small nuclear material

102
Q

Disadvantages of nuclear power

A

Public perception is negative
Nuclear waste is very dangerous and hard to dispose of
Nuclear power can cause major catastrophe e.g. Fukushima
Overall cost of building power plant is very expensive

103
Q

Specular reflection

A

When rays of light reflected evenly

104
Q

Diffuse reflection

A

When rays of light reflected unevenly

Physics (7 decks)

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