Waves Flashcards
What are the effects of microwaves on the body?
- similar frequency to the vibration of many molecules, so they can increase these vibrations. results in internal heating, the heating of molecules.
Why can’t sounds travel in space?
- its mostly a vacuum
What is the equation for frequency?
- f = 1 / T
What is ultraviolet radiation used for?
- fluorescence absorbs UV light and visible light is emitted
- used for security marking
For which waves does the doppler effect occur in?
- both longitudinal and transverse waves
What happens when the angle of incidence is equal to the critical angle?
- the emerging ray comes out along the surface. there is quite a bit of internal reflection
What can sound waves do?
- reflect
- refract
- diffract
What are microwaves used for?
- satellite communication: it can pass easily through the Earth’s watery atmosphere.
- mobile phones:
What do EM waves with higher frequencies have?
- shorter wavelengths
What is visible light used for?
- photography: camera uses a lens to focus visible light, aperture controls how much light enters the camera, shutter speed how long the film is exposed
What three things to waves have?
- amplitude
- wavelength
- frequency
What is frequency?
- the number of complete waves passing a certain point per second
- or the number of waves produced by a source each second
- measured in hertz (Hz). 1 Hz is 1 wave per second
Why does a triangular prism disperse white light?
- the boundaries aren’t parallel, meaning the different wavelengths don’t emerge parallel, so there is a rainbow effect.
How can X-rays treat cancer?
- X-rays are focused on the tumour using a wide beam
- beam is rotated round the patient with the tumour at the centre
- this minimises the exposure of normal cells to radiation
What is destructive interference?
- disturb in opposite directions and cancel each other out
Give examples of transverse waves
- most waves are transverse
- all electromagnetic waves
- ripples of water
- waves on strings
- a slinky spring wiggled up and down
What happens when two identical sets of waves meet?
- they interfere with each other
What are CT scans?
- the used X-rays to produce high res images of hard and soft tissues
What are infrared waves used for?
- remote controls: emit different patterns of infrared waves to send different commands to an appliance e.g. a TV
- optical fibres: for phone lines. can carry data over long distances very quickly
What happens when light enters a less dense medium?
- it speeds up and refracts away from the normal
What speed do all EM waves travel at in a vacuum?
- 3 x 10^8m/s
What changes the loudness of a sound?
- the amplitude
- the bigger the amplitude, the louder
What is reflection of light?
- reflection of light is what allows us to see objects
- light bounces off them into our eyes
What is diffraction?
- all waves spread out (diffract) at the edges when they pass through a gap or an object
- the amount of diffraction depend on the size of the gap relative to the wavelength of the wave
- a narrow gap is about the same size as the wavelength of the wave
What frequency range can humans hear?
- 20Hz to 20,000 Hz
What are the seven different type of waves in the electromagnetic spectrum? Order in increasing frequency and energy
- radio waves
- micro waves
- infra red
- visible light
- ultra violet
- x-rays
- gamma rays
What is period (T) ?
- the time it takes for one complete wave to pass a point
Are mechanical waves transverse or longitudinal?
- they can be both
- e.g. water waves, shock waves, waves in springs and ropes
What is the formula for wave speed?
- speed (m/s) = frequency (Hz) x Wavelength (m)
- v = f x lambda
What equation can you use with ultrasound?
- s = d x t
- distance = speed x time
What is the equation fro refractive index?
- refractive index, n = speed of light in a vacuum, c / speed of light in that material, v
- n = c / v
How long are the wavelengths for TV and FM radio?
- very short (10cm - 10m)
- must be in direct sight of transmitter
What can ultrasounds be used for?
- kidney stones are hard masses than can block the urinary tract. ultrasound beams concentrates high-energy waves at the kidney stone and turns it into sand-like particles. no need for surgery and painless
- produce a video image : can pass through the body, but whenever they reach a boundary between two different media e.g. fluid in womb and skin of foetus, some wave is reflected back and detected. timing is process on computer.
What happens when the angle of incidence is less than the critical angle?
- most of the light passes out but a little bit of it is internally reflected
How can short-wave radio signals (10m-100m) be received at long distances?
- they are reflected from the ionosphere, an electrical charged layer in the Earth’s upper atmosphere.
What is the refractive index of glass?
- it has a high refractive index of 1.5
How can you calculate how far the boundary is using ultrasound?
- time taken for reflections to reach a detector
How do endoscopes work?
- an endoscope is a thin tube containing optical fibres
- endoscopes consists of two bundles of optical fibres, one to carry light to the area of interest and one to an image back so that in can be viewed.
- can be seen through an eyepiece or displaced on a TV screen
- keyhole surgery made possible
What are x-ray used for?
- medical imaging: negative image produced
What are the effects of ultraviolet on the body?
- can damage surface cells and cause blindness
- ionising so it carries enough energy to knock off electrons in atoms
- can cause cell mutation or destruction and cancer
What is the total displacement of the waves at a point?
- the sum of the displacements
What is the doppler effect?
- when something that emits waves move towards or away from you, the wavelength and frequencies of the waves seem different
- the frequency of a source moving towards you will seem higher and its wavelength will seem shorter
- the frequency of a source moving away from you will seem lower and its wavelength will seem longer
How does ultrasound work?
- when a wave passes from one medium into another, some of the wave is reflected off the boundary between the two media and some is transmitted. this is partial reflection
this means that whenever you point a pulse of ultrasound at an object, and wherever there are boundaries between one substance and another, some of the ultrasound is reflected back
What are transverse waves?
- in transverse waves, the oscillations are perpendicular to the direction of energy transfer of the wave
How do we know that more distance galaxies are moving away faster than nearer ones?
- more distant galaxies have greater-red shits than nearer ones
they show a bigger observed increase in wavelength
What is amplitude?
- the displacement from the rest position to the crest
Are waves refracted travelling along the normal?
- no, they are not
Why does refraction occur?
- waves travel at different speeds in substances which have different densities.
- when a wave crosses a boundary between two substances, e.g. from gas to air, it changes speed
What are the effects of x-rays/gamma on the body?
- ionising and carry much mor energy than UV rays, so much more damaging and they can penetrate further into the body
- causing genetic mutation, cancer
What happens when the angle of incidence is greater than the critical angle?
- no light comes out. it is all internally reflected i.e. total internal reflection
How can long-wave radio (1-10km) be transmitted half way around the world
- long wavelength diffract around the curved surface of Earth
- it can also diffract around hill, into tunnels
What are sound waves?
- caused by vibrating objects
- mechanical vibrations are passed through the surrounding medium as a series of compression
- a type of longitudinal wave
What is wavelength (lambda)?
- the length of a full cycle of the wave
- e.g. from crest to crest
What is total internal reflection?
- a special case of refraction
What does ionising mean?
- when some radiations (UV, X-Rays and gamma) enter living cells they collide with atoms in molecules, knocking electrons off and causing ionisation. this damages/destroys cells. it may lead to tissue damage, cell mutation and cancer. may cause radiation sickness
What is refractive index?
- the refractive index of a transparent material tells you how fast light travels in the material
- every transparent material has a refractive index
What are longitudinal waves?
- in longitudinal waves, the oscillations are parallel to the direction of energy transfer of the wave
- they squash up and stretch out the arrangement of particles in material as they pass through, making compressions and rarefactions
- compressions are under high pressure (many particles ) and rarefactions are parts under low pressure
What are the effects of infrared on the body?
- can make surface molecules of any substance vibrate, causing a heating effect. if human skin is exposed to too much infrared, it may cause some skin buns
What happens when light enters a more dense medium?
- it slows down and refracts towards the normal
What do radiographers do to minimise radiation dose?
- wear lead aprons, stay behind lead screen, leave the room
- lead is also used to shield areas of the body that aren’t being scanned
What do measurements of the red-shift in galaxies suggest?
- all galaxies are moving away from us very quickly
What is red-shift?
- red shift is an observed increase in the wavelength of light coming from the galaxies and the patterns have been shifted towards the red end of the spectrum
What is the refractive index of air
- 1 (to 2 dp)
- about the same as a vacuum
What is constructive interference?
- the waves disturb in the same direction and reinforce each other
What are the properties of X-rays?
- high frequency
- high energy
- short wavelength electromagnetic waves
What are radio waves?
- EM radiation with wavelengths longer than about 10cm
Where do sounds generally travel faster in?
- solids
What is cosmic background microwave radiation (CMBR)?
- It is a form of electromagnetic radiation filling the universe
- it comes from radiation that was present shortly after the beginning of the universe
- the Big Bang is currently the only theory supporting the existence of it
What is refraction?
- all waves can be refracted ‘changing direction’
What are radio waves mainly used for?
- communication
What is gamma radiation used for?
- sterilising medical equipment: kills all microbes to sterilise them
- better than trying to boil plastic instruments , which may be damaged by high temp
- food: killing microbes and it is not radioactive after
What is the Law of Reflection?
- angle of incidence = angle of reflection
Give examples of longitudinal waves
- sound waves and ultrasound
- shock waves e.g. seismic
- slinky spring when you push the end
How can light be sent along optical fibres using total internal reflection?
- optical fibres can carry visible light over long distances
- they work by bouncing waves off the sides of a thin inner core of glass of plastic. the wave enters one end of the fibre and is reflected repeated until it emerges at the other end
- total internal reflection only happen when a wave travels through a dense substance like glass or water towards a less dense substance
What wavelength do EM waves vary from?
- 10^-15m to more than 10^4m
What is another equation to work our refractive index?
- refractive index (n) = sin i / sin r
What is the formula relating refractive index and critical angle?
- refractive index = 1 / sin C
What is the observed red-shift?
- it provides evidence that the universe is expanding and supports the Big Bang theory (that the universe began from a very small initial point)
