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physics > waves (p6) > Flashcards

waves (p6) Flashcards

doesn't include ray diagrams or wave front diagrams

1
Q

what are the two categories all waves fall into?

A

transverse or longitudinal

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2
Q

what is an oscillation/vibration?

A

waves moving up and down

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3
Q

what are transverse waves?

A

the oscillations (vibrations) are perpendicular to the direction of energy transfer
- the oscillations are up and down, but the direction of energy transfer is sideways
- not all transverse waves require a medium to travel through
- e.g. ripples on water

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4
Q

what are longitudinal waves?

A
  • the oscillations are parallel to the direction of energy transfer
  • made up of compressions (where the air particles are close together) and rarefactions (where the air particles are spaced out)
  • longitudinal waves require a medium to travel in (air, liquid, solid), as they move by by vibrating particles, and in a vacuum, there are no particles to vibrate
  • e.g. sound waves through air, which travel as particles in the air that move side to side
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5
Q

what do waves do?

A

transfer energy from one place to another

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6
Q

in both transverse and longitudinal waves, is it the wave or the air/water particles that are moving?

A

TRANSVERSE
the wave is moving, and the particles do oscillate up and down, but don’t travel through the medium

LONGITUDINAL
the wave is moving, and the particles do oscillate from side to side, but don’t travel through the medium

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7
Q

what is the amplitude of a wave?

A

the distance from the centre line (the undisturbed position) to the crest or the trough (the furthest point the wave vibrates from its undisturbed position)

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8
Q

what is the wavelength of a transverse wave?

A

the distance from one point on a wave to the equivalent point on an adjacent wave

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9
Q

what is the wavelength on a longitudinal wave?

A

measure from one compression to the next, or one rarefaction to the next

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10
Q

what is the symbol for wavelength?

A

the greek letter lambda ‘λ’

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11
Q

what is the wave frequency?

A

the number of waves passing a point each second
- unit is Hertz (Hz)
- 1 Hz = 1 wave per second

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12
Q

what is the relationship between frequency and wavelength?

A

the longer the wavelength, the lower the frequency

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13
Q

what is a period, and how do you calculate it?

A

the time (in seconds) for one wave to pass a point
- period = 1 / frequency

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14
Q

what is the wave speed, and how do you calculate it?

A

the speed at which the wave moves through the medium (ie the speed at which energy is transferred)

wave speed = frequency x wavelength
v = f x λ

v = m/s
f = Hz
λ = m

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15
Q

what method would you use to measure the speed of sound waves in the air?

A
  1. two people separated by 500m
  2. Person A holding a pair of cymbals, Person B holding a timer
  3. Person B starts timing when they see Person A clash the cymbals together
  4. Person B stops timing once they hear the sound of the cymbals clashing
  5. calculate the speed of the sound waves by dividing the distance travelled by the time taken
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16
Q

what problems and solutions are there with the method to measure the speed of waves in the air?

A
  • every person has a different reaction time, so may take extra time to start/stop the timer
  • have a large number of observers with timers, discard any anomalous results and take a mean value
  • the time between seeing the cymbals clash and hearing the sound is very short, making it difficult to press the timer at the correct times
  • increase the distance between the two people, so the time is longer, and makes it easier to start and stop the timer accurately
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17
Q

describe the three things that can happen of waves when they encounter a boundary:

A

TRANSMISSION
transmitted through the material (e.g. passes from air to glass). hasn’t changed the wave

ABSORPTION
energy of the wave is absorbed by the material. the wave may not pass through the material at all

REFLECTION
reflected off the surface of the material

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18
Q

how do you construct a ray diagram to show where an image will appear in a mirror:

A
  1. draw an incident ray from the object to the mirror
  2. draw the perpendicular normal line
  3. measure the angle of incidence, and using this, work out the angle of reflection and the reflected ray (angle of incidence = angle of reflection)
  4. draw another incident ray connecting to a different normal, and a different reflected ray
  5. extend the two reflected rays back into the mirror. where these lines meet tells us the position of the image
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19
Q

describe how ears and microphones work:

A

MICROPHONE
- key part is a paper cone
- sound waves hitting the cone causes it to vibrate
- the microphone then converts this to electrical signals

HUMAN EAR
- sound waves in the air are funnelled into the ear, where they hit the ear drum, causing it to vibrate
- three small bones transmit this info to the cochlea, which produces electrical signals that are interpreted as sound by the brain

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20
Q

describe why human hearing is limited:

A
  • sound waves in the air trigger vibrations in solids
  • only works over a limited range of frequencies
  • normal human hearing has a frequency of 20Hz to 20,000Hz
  • frequencies outside of that may not be able to make the eardrum vibrate
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21
Q

what happens when a wave passes from one medium to another?

A
  • its speed can change
  • wavespeed = frequency x wavelength, so as wavespeed changes (when passing from one medium to another), wavelength also changes, as frequency must remain constant
  • frequency doesn’t change, as waves would have to be destroyed or created at the boundary, and that’s not possible
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22
Q

do sound waves travel faster in solids or gases?

A
  • travel faster in solids
  • the particles are closer together, meaning vibrations can pass more easily between them
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23
Q

describe the relationship between frequency and pitch:

A

high frequency = high pitch
low frequency = low pitch

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24
Q

describe the relationship between amplitude and sound:

A

small amplitude = quiet sound
large amplitude = loud sound

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25
Q

what is a reflected sound wave called?

A

an echo

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26
Q

how can we view the features of sound waves?

A

connect a microphone to a cathode ray oscilloscope. however, it represents them as if they were transverse, which is incorrect (they’re longitudinal)

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27
Q

what is ultrasound?

A

soundwaves with a frequency higher than the upper limit of human hearing, so higher than 20,000Hz

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28
Q

how can ultrasound be used to image internal organs?

A
  • ultrasound waves partially reflect, meaning some waves are transmitted, and some are reflected
  • if we know the time taken for the ultrasound wave to leave the probe, bounce off the internal organ, and then be re-detected by the probe, we can calculate the distance between the probe and the internal organ
  • works for any organ not surrounded by bone
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29
Q

how can ultrasound be used in industrial imaging?

A
  • used to detect hidden defects or problems with a weld
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30
Q

describe the internal structure of the Earth:

A
  • crust (solid, thin, around 50km)
  • mantle (solid - upper mantle can flow slowly, but still classed as solid)
  • outer core (liquid)
  • inner core (solid)
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31
Q

how can earthquakes help us understand the structure of the interior of the Earth?

A
  • earthquake happens
  • causes seismic waves, carrying energy away from the earthquake
  • pass through the Earth, can be detected by seismometers in different countries
  • the patterns of these waves gives us info about the interior of the Earth
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32
Q

what are P waves (type of seismic wave)?

A
  • longitudinal, can pass through both solids and liquids
  • travel faster than S waves
  • P-wave shadow zones (much less area than S-wave shadow zones) are due to the fact that P waves travel faster in solids than in liquids
  • P waves slow down as they enter the liquid outer core, causing them to refract. they also refract when they leave the outer core
  • confirms that the outer core is liquid
33
Q

what are S waves?

A
  • transverse, can only travel through solids
  • completely avoids outer core (can’t pass through liquid), so forms an area where they can and can’t be detected. where they can’t be detected is the S-wave shadow zone
  • tells us that the Earth must have a liquid core
34
Q

why do seismic waves travel in curved paths?

A

due to density changes in the Earth

35
Q

what are electromagnetic waves?

A
  • transverse waves
  • transfer energy from the source of the waves to an absorber (e.g. microwave, transfers energy from microwave to food)
  • an example is visible light
36
Q

what happens when we pass white light through a prism?

A

splits into a spectrum of many colours. each colour of light has a different wavelength and frequency

37
Q

describe the electromagnetic spectrum:

A
  • the red end has a lower frequency and a longer wavelength. it’s the opposite at the violet end
  • goes in the order of the colours of the rainbow from left to right
  • continous spectrum: the cut-off between one type of wave and the next is unclear
  • from the left: radio waves, microwaves, infrared, visible light, ultraviolet light, x-rays, and gamma rays
38
Q

can electromagnetic waves travel in a vacuum?

A
  • transverse, therefore don’t require particles to vibrate
  • can travel in a vacuum
  • all electromagnetic waves travel at the same speed in a vacuum: 300,000,000 m/s
39
Q

describe microwave and light ray transmission, absorption, and reflection patterns:

A
  • microwaves are absorbed by foods containing water molecules
  • microwaves are reflected from metals
  • light waves are absorbed by black surfaces
  • light waves are reflected by shiny, metallic surfaces
40
Q

describe refraction:

A

where waves change direction when they change speed, when moving from one medium to another.
- for example, when light passes from air into glass, the velocity decreases, causing the direction of the waves to change. when passing out, it’s once again refracted, making the image seem as if it’s shifted position

41
Q

describe the acronym FAST:

A
  • when waves get FASTER, they move AWAY from the normal
  • when waves get SLOWER, they move TOWARDS the normal
42
Q

what is the exception to the rule of refraction?

A

any waves entering or leaving the medium at right angles to the surface (along the normal) don’t change direction

43
Q

what is a wavefront?

A
  • imagine a group of identical waves travelling together, creating a 3D shape
  • the wavefront is an imaginary line that connects all the same points in a set of waves
  • makes it easier to visualise lots of waves moving together, even with simple the wavefront lines
44
Q

describe refraction using wavefronts:

A
  • light waves moving from air into glass
  • when the first wavefronts move into the glass, those parts slow down, therefore their wavelength decreases (get closer together)
  • ## causes them to change direction towards the normal - refraction
  • wave fronts approaching the glass along the normal
  • they slow, and their wavelength decreases, but the whole wavefront slows down at the same time, meaning it doesn’t change direction
45
Q

what are the two ways electromagnetic waves can be emitted from atoms?

A
  • heating atoms (supplying it with EM waves) causes electrons to move up an energy level
  • when it returns to its original energy level, it emits an EM wave, e.g. light
  • gamma rays can be emitted from the nucleus of radioactive atoms
  • once it’s been emitted, the nucleus has less energy than at the start
46
Q

what are the hazards of ultraviolet, x and gamma rays?

A
  • potentially hazardous to the human body

ULTRAVIOLET increases the risk of skin cancer, causes it to age prematurely
X-RAYS + GAMMA RAYS are ionising radiation (knock electrons off atoms when absorbed). can cause the mutations of genes and potentially cancer

47
Q

describe the transmission and absorption of radio waves:

A
  • radio waves produced when electrons oscillate in electrical circuits
  • these radio waves can be absorbed, e.g. by an electrical circuit in an aerial
  • this causes electrons in this circuit to oscillate, creating an alternating current with the same frequency as the radio waves
48
Q

describe the uses of radio waves:

A
  • transmit radio and terrestrial TV (received using an aerial) signals
  • can travel long distances before being absorbed (e.g. by buildings/trees)
  • can also spread out between hills (diffraction)
  • can reflect off a layer of charged particles in the atmosphere
  • these all allow us to send radio waves very long distances around the Earth
49
Q

describe the uses of microwaves:

A
  • heat food - most foods contain water molecules, which absorb the energy of microwaves, causing the temperature of the food to increase
  • used to communicate with satellites in space (can pass through the Earth’s atmosphere without being reflected/refracted)
50
Q

describe the uses of infrared waves:

A
  • emitted by electrical heaters, used to cook food in ovens
  • energy of infrared is easily absorbed by the surface of objects
  • also used in infrared cameras (e.g. to check buildings for heat losses)
51
Q

describe the uses of visible light:

A
  • communication using fibre optics
  • optical fibres are very thin strands of glass, and we can transmit pulses of light down these to carry information
  • carry telephone and cable TV signals
  • visible light has a short wavelength, so optical fibres can carry a lot of info
52
Q

describe the uses of ultraviolet:

A
  • energy efficient lightbulbs
  • the ultraviolet light is created inside the bulb, then absorbed by the internal surface of the bulb and converted to visible light (transfers a greater proportion of electrical energy into light energy than filament bulbs)
  • ## short wavelength, so it carries more energy than visible light
  • sun tanning (e.g. sun bed)
53
Q

describe the uses of X-rays and gamma rays:

A
  • both used for medical imaging. very penetrative
  • x-rays can visualise broken bones (absorbed by bones)
  • ## gamma rays can detect cancers
  • can also be used in medical treatments (e.g. to treat cancer)
54
Q

describe convex lens:

A
  • have the bulgy shape (thicker at the centre than at the edges)
  • the symbol is a line with an arrow at each end
  • make light rays converge (come together)
55
Q

what is the key feature of all lenses?

A

all refract light. when light enters, it bends towards the normal, and then away from the normal when it passes out

56
Q

what is the principle axis on a convex lens diagram?

A
  • the central ray passes through the lens without being refracted (passes directly along the normal)
57
Q

what is the principle focus and the focal length on a convex lens diagram?

A

PRINCIPLE FOCUS
- all other rays refract, and are focused on a point after the lens
- called the principle focus (F)

FOCAL LENGTH
the distance from the centre of the lens to the principle focus
- different convex lenses have different focal lengths depending on the strength of the lens

58
Q

how would you produce a ray diagram for a convex lens?

A
  1. draw a ray passing from the top of the object through the centre of the lens without changing direction
  2. draw another line from the top of the object, running parallel to the principle axis. when the line hits the lens, it’s refracted through the principle focus
    - where the two lines meets shows the top of the image
59
Q

what are the three key features of an image that you must describe?

A
  1. magnified or diminished (bigger or smaller)
  2. inverted or upright (upside down or right side up)
  3. real or virtual image (can it be projected onto a screen or not)
60
Q

what are the properties of an object over 2 focal lengths away from the lens?

A
  • diminished
  • inverted
  • real
61
Q

what are the properties of an object between 1 and 2 focal lengths away from the lens?

A
  • magnified
  • inverted
  • real
62
Q

what are the properties of an object less than 1 focal length away from the lens?

A
  • magnified (this is how magnifying glasses work)
  • upright
  • virtual (the rays don’t actually meet at a point, this is the only time a convex lens produces a virtual image. shown using dotted lines, which don’t actually represent the path of the rays)
63
Q

how do you calculate the magnification of a lens?

A

magnification = image height / object height

64
Q

describe a concave lens:

A
  • thicker at the edges than in the centre (caves inwards)
  • represented with a line, and inverted arrows on either end
  • make light rays diverge (spread out)
65
Q

describe where the principle focus is on a concave lens ray diagram:

A
  • light rays run parallel to each other until they hit the lens, when they diverge
  • plotting the lines behind the lens means they come to a point, which is the principle focus
  • however, the lens isn’t actually focusing the light at the principle focus, they only appear to be coming from it
66
Q

how would you draw a ray diagram for a concave lens?

A
  1. draw a ray passing from the top of the object through the centre of the lens without changing direction
  2. draw another parallel ray from the top of the object, this passes through the lens and is refracted outwards. it must appear to have come from the principle focus, so draw a dotted line connecting the two
  3. where these lines meet shows the position of the image
67
Q

what image will a concave lens always produce?

A
  • virtual image (dotted line). only appear to cross there
  • diminished
  • upright
68
Q

what is specular reflection?

A
  • on the surface of a mirror, all the light rays are reflecting in a single direction, as the angle of incidence must equal the angle of reflection
  • this takes place on smooth surfaces
  • produces an image
69
Q

what is diffuse reflection?

A
  • light can reflect off a rough surface
  • the light rays are scattered
  • doesn’t produce an image
70
Q

describe coloured filters:

A
  • work by absorbing specific wavelengths and transmitting other wavelengths
  • red filter, for example. shine white light onto it, and it will absorb all the colours of visible light, apart from red, so only that is transmitted through
71
Q

what is the difference between transparent and translucent objects?

A

transparent: we can easily see through them
translucent: scatter the light rays, so we can’t see through them clearly

72
Q

what determines the colour of an opaque object?

A
  • white objects appear white because they reflect all of the wavelengths of visible light equally
  • black objects appear black as they absorb all the wavelengths of visible light
  • red objects absorb all of the colours of white light apart from red, which is reflected, giving it a red colour
73
Q

what happens if we combine coloured objects with coloured filters?

A
  • red object and a red filter, for example
  • the red filter absorbs all of the colours of white light, apart from red, which is transmitted
  • ## the red light now reflects off the read object, so it appears red
  • green object and red filter
  • red filter allows red light to be transmitted
  • the green object completely absorbs the red light, so none is reflected
  • the green object will appear black, as it’s reflecting no light at all
74
Q

describe which objects emit and absorb infrared radiation:

A
  • matte black surfaces are the best absorbers and emitters of infrared radiation
  • all objects, no matter what temperature, emit and absorb infrared radiation, but hotter objects will emit more infrared radiation in a given time, compared to cooler objects
75
Q

describe the relationship between temperature and wavelength and intensity of radiation:

A
  • very hot objects emit shorter wavelength radiation than cooler objects, which is more intense
  • this is why very hot objects produce visible light, as they’re so intense (the hotter the object, the whiter it is, as it has a short wavelength and is closer to the violet end of the spectrum)
76
Q

describe a perfect black body:

A

absorbs all of the radiation incident on it. none is reflected, none is transmitted
- an object that absorbs radiation well will also emit radiation well, therefore, it’s also the best possible emitter of radiation

77
Q

describe the relationship between an object’s temperature and its absorption and emission of radiation:

A
  • if an object is warmer than its surroundings, it will emit more radiation than it absorbs, and its temperature will decrease
  • if an object is cooler than its surroundings, it will absorb more radiation than it emits, and its temperature will increase
  • if an object is at a constant temperature, it’s absorbing radiation at the same rate as it is emitting radiation
78
Q

how does radiation affect the temperature of the Earth?

A
  • absorbing or emitting radiation is the only way the Earth can gain or lose energy
  • the sun emits short wavelength radiation, e.g. visible light/ultraviolet. this radiation travels to the Earth, and some is reflected by the clouds, and the remaining is then absorbed by the surface of the Earth, causing its temperature to increase
  • the Earth now emits infrared radiation back into space, however, some of this energy is trapped by greenhouse gases in the atmosphere
  • more heat energy is trapped in the atmosphere, and less is radiated into space
79
Q

why do cloudy nights tend to be warmer than clear nights?

A

clouds can reflect infrared back to Earth and prevent it from being radiated into space

physics (8 decks)

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