Waves Flashcards
What is a wave?
Disturbance caused by oscillating source that transfers energy & info in the direction of wave travel, without transferring matter
What is amplitude?
Wave’s maximum disturbance from its undisturbed position
Illustrate amplitude on a wave
What is wavelength?
Distance between the same point on two adjacent waves
Illustrate wavelength on a wave
What is frequency?
Number of complete waves passing a certain point per second
What is frequency measured in?
Measured in hertz (Hz)
What does 1 Hz mean?
1 Hz is 1 wave per second
In transverse waves, what are oscillations (vibrations) like?
Oscillations (vibrations) are perpendicular (at 90°) to direction of energy transfer
Give 3 examples of waves that are transverse
- All electromagnetic waves e.g. Light
- Ripples and waves in water
- A wave on a string
In longitudinal waves, what are oscillations (vibrations) like?
Oscillations are parallel to the direction of energy transfer
Give 2 examples of longitudinal waves
- Sound waves in air e.g. Ultrasound
- Shock waves e.g. Some seismic waves
Longitudinal waves have areas of ______ and ______
Compression and rarefraction
Sound waves are _______ and ________ waves
longitudinal and mechanical waves
What is wave speed?
The speed at which energy is being transferred (or speed wave is moving at)
All waves can be ______, ______ or ______ at the boundary between two different materials
Absorbed, Transmitted or Reflected
When waves are absorbed by material, what happens (energy wise)?
Energy is transferred into material’s energy store (e.g. How microwaves work)
What is meant when waves are transmitted?
Waves carry on travelling through new material - often leads to refraction
What is a period of a wave?
Amount of time it takes for a full cycle of the wave to pass a point
What is a wave front?
Is the locus of points in the same phase
Why can waves undergo refraction?
Due to a change in wavelength
What is the rule for all reflected waves?
Angle of incidence = Angle of reflection
What is the angle of incidence?
Angle between incoming wave and the normal
What is the angle of reflection?
Angle between reflected wave and the normal
What is the normal?
An imaginary line that’s perpendicular to the surface at the point of incidence (point where wave hits boundary)
When is a wave refracted?
When wave crosses boundary between materials at an angle, it changes direction
How much a wave refracts depends on…
- How much the wave speeds up or slows down
- Which depends on density of two materials
The higher density of material = _____ wave travels through it
slower
When wave crosses a boundary and slows down, it bends _____ the normal
Slow = TOWARDS the normal
When wave crosses a boundary and speeds up, it bends _____ ___ the normal
fast = AWAY from the normal
What changes when a wave refracts?
Wavelength of wave
What stays the same when a wave refracts?
Frequency stays the same
What will happen if a wave travels along the normal?
It will change speed but NOT be refracted
What is the optical density of material?
A measure of how quickly light can travel through it
Higher optical density = ….
slower light waves travel through it
Describe how you can construct a ray diagram to show refraction with an aid of a diagram
- Draw boundary line & normal (90° to boundary)
- Draw incident ray that meets normal at boundary + angle of incidence
- Draw refracted ray on other side of boundary
- If 2nd material is more opictially dense than 1st = angle of refraction < angle of incidence
- If 2nd material is less opictially dense than 1st = angle of refraction > angle of incidence
What is diffraction?
Spreading of waves when they pass through (narrow) gap or move past (edge of) obstacle
When does diffraction take place?
When wavelength of wave is comparable to size of obstacle or gap
Waves passing through gap/past edge of obstacle spread out without changing their… (name 3 things)
- Wavelength
- Speed
- Frequency
Wider gap = …
less waves spread out (the smaller the diffraction)
Narrower gap = …
more the waves spread out (the greater the diffraction)
Illustrate diffraction of waves through a wide gap
Illustrate diffraction of waves through a narrow gap
Illustrate diffraction of waves at an edge
Name 3 real life examples of where diffraction is used
- Optical instruments
- Ultrasound waves in medicine
- Radio wave reception
Explain how ultrasound waves in medicine work
Spread out from hand-held transmitter & reflect from tissue
boundaries inside womb
What happens if the transmitter is too narrow?
Waves spread out too much = image becomes too faint
What are narrow telescopes for?
Closer stuff
Explain how diffraction is used in the Hubble Space Telescope
- Small amount of light passes through Hubble Space Telescope = small amount of diffraction occurs
- Because telescope is so wide
- Images are clear and detailed
Why do people who in hilly areas have poor TV reception?
Radio waves passing top of hill are diffracted by hill but they don’t spread enough behind the toll
What are electromagnetic waves?
Transverse waves → transfer energy from a source to an absorber
All EM waves travel at the ____ ______ through ___ or _____
Travel at the same speed through air or vacuum (space)
EM waves form _____ _______ over a range of _________
continuous spectrum over a range of frequencies
How are EM waves grouped? (3x)
Based on their wavelength, frequency and energy
Recite the order of EM waves within the spectrum (from low freq. to high freq.)
What do the wavelengths of the electromagnetic spectrum range from?
10-15 m to 104 m and beyond
Why is there such a large range of frequencies of EM waves?
Because EM waves are generated by a variety of charges in atoms and their nuclei
Shorter wavelength = ….
higher its frequency = higher the energy
How is visible light detected?
By our eyes
How do we see the different wavelengths of visible light as?
As different colours
What 4 EM waves are used for communication?
- Radio waves
- Microwaves
- Infrared
- Visible Light
What are radio waves?
EM radiation - wavelength longer than 10 cm
Why can long-wave radio waves (1-10 km) be transmitted from e.g. London to halfway round world?
Because long wavelengths diffract (bend) around curved Earth surface i.e. they can diffract around hills, into tunnels, etc.
∴ Radio signals can be received even if receiver isn’t in line of
the sight of transmitter
Why can short-wave radio signals (10m-100m) be received long
distances from a transmitter?
Because they’re reflected from the ionosphere
How does Bluetooth work?
Uses short-wave radio waves to send data over short distance between devices without wires
Medium-wave signals (shorter ones) can relate from ionosphere depending on _______ ________ and ____ of day
depending on atmospheric conditions and time of day
What kind of wavelength do radio waves that are used for TV and FM radio transmissions have?
Very short wavelengths
To get reception why must TV and FM radio transmissions signals be in direct sight of the transmitter?
Signal doesn’t bend or travel far though buildings
Name 3 uses of radio waves
- TV
- Radio Systems
- Bluetooth
Name 2 uses of microwaves
- Mobile phones
- Satellite television systems
Why does communication to and from satellites use microwaves?
They can easily pass through earth’s watery atmosphere
Why is there a slight time delay between signal being sent and received?
∵ of long distance signal has to travel
Why are microwaves used to beam signals from one place to another and not radio waves?
∵ they don’t spread as much as radio waves
Name 3 uses of infrared
- TV remote controls
- Night vision devices
- Heating
What does absorbing IR radiation cause objects to get?
Hotter
How can food can be cooked using IR radiation?
Temperature of food increases when it absorbs IR radiation
What does every object do (regarding IR radiation)?
They absorb and emit infrared radiation
Why do all objects emit IR radiation?
∵ of motion of their particles
Hotter object is = more …
IR it radiates in given time
What does the amount and frequency of emitted raditation depend on?
Temperature and surface of object
What do objects at constant temperature do?
Emit IR radiation at same rate that they absorb it
What does an object that’s hotter than its surroundings do?
Emits more IR radiation > than it absorbs as it cools down
What does an object that’s cooler than its surroundings do?
Absorbs more IR radiation > than it emits as it warms up
Dark, matt surfaces are ___ ____ and ___ ____ of infrared radiation
good absorbers and good emitters
Light, shiny surfaces are ____ ______ and ___ _____ of infrared radiation
poor absorbers and poor emitters
Light, shiny surfaces are ___ _______ of infrared radiation
good reflectors
As an object heats up, what does it do?
Radiates more infrared radiation, at higher frequencies
What is black-body radiation?
Range of electromagnetic radiation emitted by an object at a particular temperature
What is a perfect black body?
Object that absorbs all of radiation that hits it, no radiation is transmitted or reflected
What happens if the atmosphere absorbs more radiation without emitting same amount?
Overall temperature will rise until absorption and emission are equal (global warming)
Name 2 uses of visible light
- Fibre optic communications
- Photography
What are optic fibres?
Thin glass or plastic fibres that carry data over long distances as pulses of visible light
How do fibre optic cables use visible light to transmit data?
- Work because of reflection → light rays are bounced back and forth until they reach end of fibre
- Light is not easily absorbed or scattered as it travels along fibre
Name 2 uses of UV
- Security pens
- Artificial tans
How does security marking work?
- Security pens → mark property with name
- Under UV light ink will glow (fluoresce) but it’s invisible otherwise
- Helps police identify your property if it’s stolen
What are X-rays used for?
Medical imaging - to see if a person has broken bones
How do X-rays work?
- X-rays transmit easily through flesh but very easily through denser material like bones/metal
- Starts off as white
- White = x-rays absorbed
- Black = x-rays transmitted
Name 2 uses of gamma rays
- Sterilising surgical instruments
- Killing harmful bacteria in food
What is the problem with low energy waves?
Have a heating effect
What is the problem with high energy waves?
Have enough energy to cause ionisation
What is the danger of microwaves?
Heating of body tissue
What is the danger of infrared?
Skin burns
What are the dangers of ultraviolet? Name 2
Skin cancer and blindness
What is the danger of X-rays?
High doses kill cells
What is the danger of gamma rays?
Genetic mutations
What radiographers do to protect themselves from the effects of gamma rays/x-rays?
X-rays affect a photographic lm in the same way as ____
light
Name 4 things X-rays are used in
- CT scanning
- Bone fractures
- Dental problems
- Killing cancer cells
How can X-rays and gamma rays be used to treat people with cancer?
∵ high doses of these rays kill all living cells → they’re carefully directed towards cancer cell
Why is gamma radiation used as medical tracer?
Can pass out through body to be detected
What are sound waves?
Longitudinal waves and cause vibrations in medium, which are detected as sound
Why can’t sound waves travel in space?
There’s no particles to move/vibrate
What is the range of human hearing?
20 Hz to 20 000 Hz
How is the pitch of sound determined?
By frequency of vibrations of source
How is the loudness of sound determined?
Size of amplitude of disturbance
Sounds can ____, _____ & ____
Reflect, refract and diffract
What reflects sound waves?
Hard flat surfaces
What are echoes essentially?
Reflected sound waves
What is ultrasound?
Ultrasound is a sound with frequencies higher than 20 000 Hz
Explain how electronic systems can be used to produce ultrasound
- Electrical devices can produce electrical oscillations of any frequency
- Then conserved into mechanical vibrations to produce sound waves beyond range of human hearing
Ultrasound waves get ____ _______ at boundaries between two different media
partially reflected
What is meant by partial reflection?
When wave passes from 1 medium into another:
- Some of wave reflected off boundary
- & some is transmitted (and refracted)
How can we use the partial reflection in ultrasound?
Time taken for reflections to reach a detector can be used to measure how far away boundary is
Name 3 uses of ultrasound
- Prenatal scanning
- Removal of kidney stones
- Finding flaws in objects (like pipes or materials)
Explain how ultrasound can be used in prenatal scanning
- Ultrasound waves → pass through body but when reach boundary between two different media (e.g. fluid in womb and skin of foetus) = some of wave reflected back & detected
- Exact timing + distribution of these echoes → processed by computer
- → produces video image of foetus
Explain how ultrasound can be used in finding flaws in objects like pipes or materials
- Ultrasound waves entering material → reflected by far side of material
- If there’s flaw (e.g. Crack inside object) = wave will be reflected sooner
What can CT scans do?
Distinguish between different types of soft tissue as well as between bone and soft tissue
Explain how CT scans work
- Take range of X-ray images from various position
- → processed by computer to build 3D image of inside of patient’s body
Name 3 pros of CT scans
- Lets doctor gain much greater insight into what’s wrong with patient
- Only method that provides detailed images of bone, soft tissue, blood vessels
- Painless
- Widely available
Name 3 cons of CT scans
- Exposure to radiation
- Allergic reaction to contrast material
- Misinterpreted test results
How can you can measure risk of radiation?
Using Radiation Dose in Sieverts
What does risk depend on?
Total amount of radiation absorbed and how harmful the type of radiation is
How is ultrasound used remove kidney stones?
- Powerful ultrasound waves used to break kidney stone into bits
- Fragments are then small enough to leave kidney naturally
When something moves towards you, what happens to the wavelength and frequency of sound?
Wavelength decreases and frequency increases
When something moves towards you, what happens to the pitch of sound?
Becomes higher
When something moves away from you, what happens to the wavelength and frequency of sound?
Wavelength increases and frequency decreases
When something moves away from you, what happens to the pitch of sound?
Becomes lower
What an image produced in a plane mirror like? (name 3 things)
- Virtual
- Upright
- Laterally inverted
What can the refraction by a prism lead to? (2x)
Dispersion of light waves and formation of a spectrum
When does total internal reflection occur?
Angle of incidence in denser medium > critical angle
How is visible light and infrared transmitted through optical fibre via?
Total internal reflection
What are optical fibres used for? (2x)
- Communication technology
- Medicine e.g. endoscope
What is an endoscope used for?
To see inside body cavity without cutting body open
Explain how an endoscope works
- Contains 2 bundles of optical fibres
- Used to shine light into cavity
- Transmit light back so surgeon can see internal surface of cavity
- Tiny lens = image at the end of fibres (seen directly or using camera)
Name 2 benefits of optical fibres
- Can carry more info than ordinary cable of same thickness
- Signals in optical fibres don’t weaken as much over long distances as signals in ordinary cables
- Don’t need to be amplified as often as signals in copper cables
How does a lens form an image?
By refracting light
What happens to light in a convex lens?
Bulges outwards - causes rays of light parallel to axis to be brought together (converge) at principal focus
What happens to light in a concave lens?
Cave inwards - causes rays of light parallel to axis to spread out (diverge)
What is the focal length?
Distance form centre of lens to principal focus
To describe an image properly, what are the 3 things you need to say?
- How big it is compared to object
- Whether it’s upright or inverted (upside down) relative to object
- Whether it’s real or virtual
What is a real image?
Where light from an object comes together to form an image on a ‘screen’ (e.g. eye’s retina)
What is a virtual image?
When rays are diverging so light from the object appears to be coming from a completely different place
Give 2 examples of virtual image
- Image of your face in a mirror
- Image gottenvwhen looking at an object through a magnifying lens
What type of lens do magnifying glasses use?
Convex Lenses
Object being magnified must be _____ to lens than the ____ length
Closer to lens than the focal length
What’s a useful pharse to use in exam if they ask you about virtual images?
“you can’t project a virtual image onto a screen”
Name 7 parts of the eye
- retina
- variable focus lens
- cornea
- pupil
- iris
- ciliary muscle
- suspensory ligaments
What is the retina?
Light sensitive cells at back of your eye
What is the function of the retina?
Where lens will focus light rays from object and real image will be formed
What’s the function of the variable focus lens?
Focuses light into retina
What’s the function of the cornea and what is it?
Transparent layer that protects eye & helps to focus light into retina
What’s the function of the pupil and what is it?
Central hole formed by iris - light enter eye through pupil
What’s the function of the iris and what is it?
Coloured ring of muscle that controls amount of light that can enter eye
What is the function of ciliary muscles?
Causes changes in shape of lens = allow light to be focused arriving from varying distances
What do the suspensory ligaments do?
Attach ciliary muscles to the lens
Light entering the eye is refracted by what?
Cornea & Lens
What is usually the near point of a human eye?
Approximately 25 cm from the eye
What is usually the far point of a human eye?
Infinity from the eye
What can the eye focus on? (objects between…)
Objects between near point and far point
What meant by the range of vision?
Distance between the near point and far point
What is long-sightedness caused by?
Eyeball being too short OR eye lens being unable to focus a sharp image on the retina
What is short-sightedness caused by?
By eyeball being too long OR eye lens being unable to focus a sharp image on the retina
Where does long-sightedness cause the image to form?
Behind retina
Where does short-sightedness cause the image to form?
Before retina
How can long-sightedness be corrected?
By using a convex (convering) lens
How does a convex lens correct long-sightedness?
Causes light rays to converge slightly before they hit lens = they refract perfectly onto retina
How can short-sightedness be corrected?
With concave (diverging) lens
How does a concave lens correct long-sightedness?
Light rays diffract outwards slightly as they pass lens = focused exactly on retina by lens in eye
What are lasers?
Concentrated sources of light
Name 3 uses of lasers
Cutting, cauterising and burning
Why are lasers used in eye surgery?
To correct visual defects
In the eye, the image is brought to focus on retina by changing the shape of the lens. What is the camera equivalent?
Image is brought to focus on film or CCD sensor by varying the distance between flim and lens
What is the camera equivalent of the retina?
Film or CCD sensor
