Waves, EM Spectrum and Radiation Flashcards
Amplitude of a wave
Displacement from rest position to trough / crest
Wave length in a wave
Length of a full cycle of one wave
Frequency of a wave
Number of complete cycles of a wave per second
Period of a wave
How long it takes to make a full cycle
Transverse wave definition
Waves with vibrations perpendicular to the direction of travel e.g. EM waves, S-waves, waves in water
Longitudinal wave definition
Waves with vibrations parallel to the direction of travel e.g. sound waves, P-waves
Wave speed formula
Wave speed = frequency x wavelength
How to measure speed of sound
- 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
Transmission of waves through second material
Wave carries in travelling through second material
Normally leads to refraction
Reflection of waves
Wave is sent back away from the second material
Wave is absorbed by second material
Wave transfers energy to material’s energy store e.g. transferred to thermal energy like in a microwave
Refraction
When waves change direction when entering a material of different density at an angle
What happens to the wave when the second medium is denser?
Bends towards the normal as it slows down
What happens to the wave when the second medium is less dense?
Bends away from the medium and speeds up
The shorter the wavelength of an EM wave..
The more it will bend
What are sound waves and what causes them?
Longitudinal waves
Series of compression and rare fractions caused by vibrating objects
Factors affecting what frequencies of sound can transfer through an object
Object size
Object shape
Object structure
Order of which medium sound travels in fastest (fastest to slowest)
Solid
Liquid
Gas
Why can’t we detect the refraction of sound waves?
Sound waves spread out so much that we cannot see the change in direction
Why can’t sound travel in vacuums?
There are no particles that vibrate to allow sound to travel
What happens when sound tries to travel through flat, hard surfaces?
They will be reflected and cause echoes
How we hear sounds method
- 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
Definition of ultrasound
Sound with frequencies over 20,000 Hz
How are ultrasounds generated?
Electrical devices generate electrical oscillations of any frequencies and are converted and produced by mechanical vibrations
Uses of ultrasound
Medical imaging
Industrial imaging
Echo sounding
How does medical imaging work?
- 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
How does industrial imaging work?
- 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
How does echo-sounding work?
- 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
Infrasound definition
Sound with frequencies lower than 20Hz
Uses of infrasound
Communication between animals e.g. whales
Produced by natural events e.g. earthquakes so they can be predicted
Exploring the structure of the Earth
P-waves facts
Longitudinal
Can travel through solids and liquids
Faster than S-waves
S-waves facts
Transverse
Only travel through solids
Slower than P-waves
How to calculate angle of reflection
Angle of reflection = angle of incidence (angle bateen incident ray and the normal)
Speculate reflection definition
When light is reflected on a flat, smooth surface
Diffuse reflection definition
When light is reflected on a touch surface so waves are reflected on all kinds of directions
Why are objects white?
They reflect back all wavelength of visible light equally
Why are objects black?
They absorb all wavelengths of visible light
Why are objects translucent or transparent?
They transmit some, most or all and the light passes through them
Why are objects certain colours?
They absorb all other wavelengths of light except one, which they reflect
How do colour filters work?
- 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
EM waves facts
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
7 parts of the EM spectrum
Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays
Effect of radio waves on human health
-radio waves pass through the body
Effect of microwaves on human health
Some can be absorbed, heating cells and can be dangerous
Effect of infrared on human health
Mostly reflected or absorbed by skin, causing some heating and can cause burns when too hot
Effect of ultraviolet on human health
Absorbed by skin
Ionising
Can cause skin cancer, eye conditions and blindness
Effect of X-rays and gamma rays on human health
Highest frequencies, so more energy and more damage can be caused
Passes through skin so deeper tissues are affected
What are colour is the best emitter of radiation?
Black
How are radio waves generated?
- alternating current in a circuit has electrons that oscillate to create radio waves
- radio wave has same frequency as electric current that made it
Uses of radio waves
- 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
Microwaves and radio waves in satellites
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
Uses of microwaves
- 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
Uses of infrared
- Infrared cameras
- thermal imaging
- infrared sensors
- electric heaters
- optic fibres
- TV remotes
Uses of visible light
- seeing
- photography
Uses of UV
- fluorescent lights
- security pens
- banknotes and passports
- sterilisation of water (kills bacteria)
Uses of X-rays
- X-ray images
- medical imagery
- security
Uses of gamma rays
- sterilising food and equipment
- medical imaging (PET scans)
- cancer treatment
How does movement of electrons generate radiation?
- 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
How does an atom lose electrons?
It absorbs enough energy that it moves so far that it leaves the atom
This makes the atom an ion and has been ionised
Ionising radiation definition
Any radiation that can knock off electrons from atoms
Isotope definition
Same element of an atom that has a different mass number
What is mass number?
Amount of protons and neutrons
What is atomic number?
Amount of protons
Isotope facts
Usually less stable than elements
Tend to decay and emit radiation
Elements usually only have 1 or 2 stable isotopes
What are alpha particles?
Helium nuclei
What is alpha radiation?
When an alpha particle is emitted from the nucleus
Alpha particles facts
Low penetration (stopped by few cm of air, sheet of paper) Strongly ionising (due to size)
What are beta particles?
Fast-moving electrons / positrons
What is beta radiation?
When beta particles are emitted by the nucleus.
Beta particles facts
Moderate penetration (stopped by few metres of air, 5mm of aluminium) Moderate ionisation
What is gamma radiation?
Radiation emitted from the nucleus due to nuclear rearrangement
Gamma radiation facts
High penetration (stopped by thick sheets of lead, metres of concrete) Weakly ionising
What happens in beta-minus decay?
Neutron changes into a proton and electron
Electron gets emitted and proton stays
What happens in positron emission?
A proton changes into a neutron and positron
Positron is emitted and neutron stays
What happens in neutron emission?
A neutron gets emitted
Why can’t you predict when an isotope will decay?
Radioactivity is random
What is activity measured in?
becquerels (Bq)
Definition of half-life
Average time taken for number of radioactive nuclei in an isotope to halve
How to find half-life on a graph
Time taken for activity to halve
Background radiation definition
Low-level radiation that’s around us all the time
Background radiation examples
- 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
Irradiation definition
Exposure to radiation
How to prevent irradiation?
- 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
Contamination definition
Radioactive particles getting onto objects
How to prevent contamination?
- wearing gloves and using tongs when handling radioactive substances
- wearing protective suits to prevent them from breathing particles in
How does radiation damage cells?
- 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
Uses of alpha radiation
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
Uses of gramma radiation
- sterilisation of food
- sterilisation of medical equipment
Uses of radioactive tracers
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
Radiation in thickness gauge
- 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
PET scan method
- 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
Alpha radiation in treating tumours
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
Beta radiation in treating tumours
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
Gamma radiation in treating tumours
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
Definition of nuclear fission
The splitting up of large atomic nuclei
Chain reaction in nuclear fission method
- 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
How to control chain reactions
- 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
How do we generate energy from fission?
- 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
Nuclear fusion definition
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
Conditions for nuclear fusion and why
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)
Advantages of nuclear power
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
Disadvantages of nuclear power
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
Specular reflection
When rays of light reflected evenly
Diffuse reflection
When rays of light reflected unevenly
