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
What does an object that’s hotter than its surroundings do?
Emits more IR radiation > than it absorbs as it cools down
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
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
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
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 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
Object being magnified must be _____ to lens than the ____ length
Closer to lens than the focal length
Name 7 parts of the eye
- retina
- variable focus lens
- cornea
- pupil
- iris
- ciliary muscle
- suspensory ligaments
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
