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AQA Physics > Waves > Flashcards

Waves Flashcards

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1
Q

what are waves?

A
  • transfer energy through a medium
  • particles of the medium oscillate and transfer energy between each other= x move
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2
Q

what is a longitudinal wave?

A
  • oscillations are parallel to the direction of energy transfer
    eg. sound, p-waves, s-waves
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3
Q

what is a transverse wave?

A

oscillations are perpendicular to direction of energy transfer eg. EM waves, ripples+waves in water

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4
Q

properties of a wave

A
  • amplitude=maximum displacement of a point on a wave away from its undisturbed position
  • wavelength=distance from a point on one wave to the equivalent point on the adjacent wave
  • frequency=number of waves passing a point each second
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5
Q

what is a period?

A

the time (s) it takes for a wave to pass a point

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6
Q

period equation

A

T=1/f

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7
Q

what is wave speed?

A

speed at which the energy is transferred/wave moves through the medium

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8
Q

wave speed equation

A

v = f λ

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9
Q

how can we measure to speed of sound?

A
  1. attach a signal generator to a speaker=generate sound with a specific frequency
  2. set up the oscilloscope so that the detected waves from each microphone are shown differently
  3. put both microphones next to the speaker, then slowly move one away until the waves are aligned on the display but have moved exactly a wavelength apart
  4. measure the distance between the microphones as one wavelength
  5. use v = f λ to find wave speed
  6. speed of sound in air is 330 m/s so your results should be around that
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10
Q

required practical: ripple tank

A
  1. attach a signal generator to a dipper of a ripple tank to create waves at a set frequency
  2. use a lamp to see wave crests on a screen below the tank. make sure the shadows are the same size as the waves
  3. a wavelength is equal to the distance between each shadow. measure the distance of shadows that are 10 wavelengths and divide by 10 to find the average wavelength
  4. use v = f λ to find the speed of the waves
    - suitable for investigating waves, measure wavelength without disturbing waves
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11
Q

how are velocity, wavelength and frequency linked (practical)?

A
  • attach one end of a string to a vibration generator, attach the a hanging mass on the other end which keeps the string taut
  • the vibration generator is attached to a signal generator, which allows us to change the frequency of vibration of the string
  • turn on the signal generator and change it to a frequency where you can see a clear wave
  • to measure the wavelength, measure the total length of the standing wave using a ruler, from the vibration generator to the wooden bridge
  • calculate wave speed with this equation v = f λ
  • when you change f, to calculate wavelength, measure no. of half-wavelengths, divide that no. by the total length and multiply by 2 to find a full wavelength
  • wavespeed depends on tautness of string and mass/cm
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12
Q

what happens when waves meet a boundary between two different materials?

A
  • absorbed - transfers energy to material’s energy stores
  • transmitted - waves carry on travelling through material
  • reflected
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13
Q

ray diagram of reflection

A
  • angle of incidence=angle of reflection
  • angle of incidence - angle between incoming wave and normal
  • angle of reflection - angle between reflected wave and normal
  • normal - imaginary line which is dotted, that’s perpendicular to surface of point of incidence
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14
Q

when does specular reflection happen?

A
  • wave is reflected in a single direction by a smooth surface=clear reflection
    eg. light hitting a mirror
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15
Q

when does diffuse reflection happen?

A
  • wave reflected in a rough surface and the reflected rays are scattered in different directions
  • normal is different for every incoming ray=angle of incidence is different on each ray
  • rough surface=appears matte+ x clear reflection
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16
Q

required practical: refraction

A
  • done in dim room to clearly see light rays
    1. place a transparent rectangular block on a piece of paper and trace it. use a ray box/laser to shine a light ray at the middle of one side of the box
    2. trace the incident ray and mark where light emerges on the other side
    3. remove the block and join the incident ray to the emerging point to get the refracted ray
    4. draw a normal at the point the ray entered the block and use a protractor to measure the angle of incidence and the angle of refraction
    5. repeat with rectangular blocks of different materials, keeping the incident angle the same
    6. the angle of refraction changes for different materials due to their optical densities
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17
Q

required practical: reflection

A
  1. take a piece of paper and draw a line across it. place an object so one of its sides lines up with the line
  2. shine a ray of light at the object’s surface and trace the incoming and reflected light beams
  3. draw the normal at the point the light hits the object
  4. use a protractor to measure the angle of incidence and the angle of reflection
  5. record width and brightness of reflected ray
  6. repeat with different objects
    smooth surfaces eg. mirrors=clear reflection, rough surfaces eg. paper=diffuse reflection=reflected beam wider and dimmer
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18
Q

what is refraction?

A

the change of direction of a wave when it crosses a boundary between 2 materials at angle

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19
Q

what does refraction depend on?

A
  • how much the wave speeds up or slows down=depends on density of the materials
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20
Q

what happens to a wave when it meets a boundary?

A
  • it slows down or speeds up=denser materials=slow down+bend towards normal
  • its wavelength changes
  • frequency stays the same
  • if wave is travelling along normal=changes speed+ x refracted
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21
Q

what is optical density?

A

a measure of how quickly light travels through a material
- high optical density=slower light waves travel through it

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22
Q

refracted ray diagram

A
  • draw boundary between the materials and the normal
  • draw the incoming ray=angle of incidence
  • draw refracted ray:
    second material=more optically dense=refracted ray bends towards normal=angle of refraction smaller than angle of incidence
    2nd material=less optically dense=angle of refraction larger than angle of incidence
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23
Q

what is the range of human hearing?

A

20 Hz to 20k Hz

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24
Q

how does sound travel?

A
  • caused by vibrating objects which are passed through the surroundings
  • faster in solids=air particles hitting the object cause its particles to vibrate, those particles then hit the particles next to them
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25
Q

why can’t sound travel through space?

A

space is a vacuum= x particles to move/vibrate

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26
Q

how do we hear?

A
  • sound waves reaches the ear drum which makes it vibrate
  • these vibrations are passed on to the ossicles –> semicircular canals –> cochlea
  • cochlea turns the vibrations into electrical signals which are sent to the brain and allow you to sense the sound
  • different materials convert different frequencies of sound waves into vibrations eg. microphones pick up sound outside the normal hearing range
27
Q

how is human hearing limited?

A
  • shape+size of ear drum
  • structure of ear parts
28
Q

how are sound waves reflected or refracted?

A

reflected
- hard flat surfaces eg. echoes

refracted
- when they enter different media
- denser material=speed up=wavelength changes+frequency stays the same

29
Q

what is ultrasound?

A
  • sound with frequencies over 20k Hz
30
Q

how are sound waves reflected at boundaries?

A
  • when a wave passes from one medium to another, some of it is reflected and the rest is transmitted+refracted
31
Q

how is ultrasound used to detect things?

A
  • the time taken for the reflections to reach a detector can be used to determine how
    far away such a boundary is
32
Q

uses of ultrasound

A
  • medical imaging=pre-natal scanning=ultrasound waves pass through the body=reach boundary between 2 media eg. fluid in womb+skin of foetus=wave is reflected back+detected=exact timing+distribution of echoes are processd by a computer to produce a video image
  • industrial imaging=find flaws in pipes or materials eg. wood/metal=ultrasound will be reflected by the far side of material=flaw eg. crack in object=wave reflected sooner
  • echo sounding use high frequency sound waves= boat/submarine detects objects in deep water+measure water depths
33
Q

how are waves used to explore structures?

A
  • earthquakes produce seismic waves which are detected by seismometers
  • when seismic waves reach a boundary between different layers of material, some will be absorbed and some will be refracted
  • when waves are refracted they change speed gradually=curved path
  • if properties change suddenly=wave speed changes abruptly=path has a kink
34
Q

types of seismic waves

A
  • P-waves are longitudinal, seismic waves=travel at different speeds through solids and liquids+faster than s-waves
  • S-waves are transverse, seismic waves=cannot travel through a liquid or gas
  • P-waves and S-waves
    provide evidence for the structure and size of the Earth’s core
35
Q

what is the EM spectrum?

A

a continuous spectrum (not an exact cut off point for each type of wave)

36
Q

what are EM waves?

A

transverse waves that transfer energy from the source of the waves to an absorber eg. microwave from oven to food

37
Q

what is the EM wave we can see?

A

visible light

38
Q

how do different materials react to EM waves?

A
  • they either absorb, transmit EM waves
    eg. visible light absorbed by black matt surfaces, reflected by shiny silver surfaces
    microwave absorbed by food with water molecules, reflected by metals
39
Q

properties of all EM waves

A

same speed through air or a vacuum eg space (3x10^8 m/s)

40
Q

the EM waves from long to short wavelength/low to high frequency

A

radio
microwave
infrared
visible light (red to violet)
ultraviolet
X-rays
gamma rays

41
Q

wavelengths of EM waves

A

radio - 1m - 10^4m
microwave - 10^-2m
infrared - 10^-5 m
visible light - 10^-7m
x-rays - 10^-10m
gamma rays - 10^-15m

42
Q

required practical: leslie cube

A
  1. place an empty leslie cube on a heat proof mat
  2. boil water in a kettle and fill the leslie cube with the water
  3. wait for the leslie cube to warm up, put a thermometer against all 4 faces of the cube, they should all be the same temp
  4. put an infrared detector 10 cm away from one of the cube’s faces and record it
  5. repeat this for all the 4 cube’s faces, ensuring the distance is the same each time
  6. the matt black face should have more infrared radiation than the white one, more for the matt ones than the shiny one
  7. repeat the experiment again
43
Q

how are radio waves made?

A
  • all EM waves are made by oscillations in electrical circuits
  • When radio waves are absorbed they create an a.c with the same frequency as the radio wave itself=radio waves can themselves induce oscillations in an electrical circuit
44
Q

what is a transmitter?

A

the object which charges oscillate to create the radio wave (which is then emitted to a receiver which absorbs the radio wave)

45
Q

how are all EM waves made?

A
  • changes in atoms and their nuclei=EM waves being generated or absorbed over a wide frequency range eg. gamma rays originate from changes in the nucleus of an atom
46
Q

uses of EM waves

A
  • microwaves – satellite communications, cooking food=
  • infrared – electrical heaters, cooking food, infrared cameras=
  • visible light – fibre optic communications=
  • ultraviolet – energy efficient lamps, sun tanning=
  • X-rays and gamma rays – medical imaging and treatments=
  • gamma rays - medical tracers=
47
Q

types of radio waves and their uses

A

long-wave radio waves (1-10 km)
- diffract around curved surfaces of the earth, hills, into tunnels=signal can be received even if receiver isn’t in line of sight of the transmitter

short-wave radio waves (10-100m)
- reflected from ionosphere
- received in long distances eg bluetooth (wireless way of sending data)

medium wave radio waves
- reflect from ionosphere depending on atmospheric conditions and time of day
- used in TV and FM radios=in direct sight of transmitter= x bend or travel far through buildings

48
Q

dangers of UV, X-rays and gamma rays

A
  • Ultraviolet waves can cause skin to age prematurely, increase risk of skin cancer, blindness
  • X-rays and gamma rays are ionising radiation that can cause mutation of genes, cell destruction and cancer
49
Q

how do lenses form images?

A

refracting light

50
Q

what is a focal length?

A

the distance from the lens to the principal focus

51
Q

convex lens

A
  • bulges outwards
  • parallel rays converge at principal focus (come together)
52
Q

concave lens

A
  • caves inwards
  • parallel rays diverge (spread out)
53
Q

what are the wavelengths of the colours in visible light?

A

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency eg. violet 400 nm, red 700 nm

54
Q

how do colour filters work?

A
  • only transmit a certain colour/s, the rest are absorbed
  • primary colour filter only transmits that colour
  • if you look at an object which colour wasn’t made up of the primary colour, its light wouldn’t be transmitted so the object will look black=light reflected by object is absorbed by filter
  • filters that aren’t for primary colours let through both the wavelengths of light that colour and the wavelengths of the primary colours that are mixed to make it
55
Q

how do we see things the colours they are? Opaque

A
  • opaque objects= objects that x transmit light
  • colour of an opaque objects depends on the wavelengths of light that are strongly reflected
  • wavelengths that are not
    reflected are absorbed
  • all wavelengths are reflected equally the object appears white
  • all wavelengths are absorbed the objects appears black
  • opaques objects that aren’t a primary colour either reflect wavelengths of the colour or are reflecting wavelengths of primary colours that mix together to make that colour
56
Q

what do transparent or translucent object do?

A

transmit light
- x absorb or reflect all light
- their colours depend on the wavelength of light transmitted and reflected by it

57
Q

what do all objects do?

A

emit and absorb infrared radiation no matter their temp is
- the hotter the body (object), the more infrared radiation it
radiates in a given time

58
Q

what is a perfect black body?

A
  • an object that absorbs all of the radiation incident on it
  • does not reflect or transmit any
    radiation
  • the best possible emitter,
    (good absorber=good emitter)
59
Q

what is intensity?

A

power per unit area

60
Q

how does a body’s temp affect intensity and distribution of wavelengths?

A
  • temp increases=intensity of every emitted wavelength increases
  • intensity increases quicker for short wavelengths=peak wavelength decreases
61
Q

what happens to an object in room temp?

A
  • absorbs radiation at
    the same rate as it emits radiation
62
Q

how does temp of an object/body increase?

A

when the body absorbs radiation faster than it emits
radiation

63
Q

how does radiation affect the earth’s temp?

A
  • radiation is transferred to earth from the sun and it’s absorbed=increase in temp=emits infrared radiation back
  • clouds reflect radiation back to earth
  • greenhouse gases trap some of the energy from radiation
  • at night, less radiation absorbed than emitted=decrease in temp
  • atmosphere absorbs more radiation without emitting the same back=overall rise in temp until absorption and emission are equal again

AQA Physics (8 decks)

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