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waves Flashcards

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1
Q

waves can either be

A

transverse or longitudinal

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2
Q

define transverse waves

A

the direction of oscillation is perpendicular to the direction of energy transfer

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3
Q

examples of transverse waves

A

electromagnetic waves like light and microwaves, ripples on a water surface

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4
Q

define longitudinal waves

A

the direction of oscillation is parallel to the direction of energy transfer

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5
Q

examples of longitudinal waves

A

sound waves travelling through air

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6
Q

difference between transverse and longitudinal waves (medium)

A

all longitudinal waves require a medium to travel through (gas, liquid, solid) whereas some transverse waves can travel through a vacuum e.g., electromagnetic waves

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7
Q

what do all waves do

A

they transfer energy from one place to another
e.g., ripples transfer kinetic energy
sound waves transfer sound energy

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8
Q

describe evidence that for ripples on a water surface and for sound waves in air, it is the wave and not the water or air itself that travels

A

ripples on a water surface: if you place a floating duck on a water wave (transverse) the duck will bob up and down but will not move from side to side

sound waves in air: if you use a slinky to model a longitudinal wave and mark a fixed point on the slinky, it will move side to side but does not travel through the medium

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9
Q

what is the top of the wave called

A

the peak or the crest

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10
Q

what is the bottom of the wave called

A

the trough

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11
Q

define the amplitude of a wave

A

the maximum displacement of a point on a wave away from its undisturbed position

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12
Q

define the wavelength of a wave

A

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

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13
Q

define the frequency of a wave

A

the number of waves passing a point each second

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14
Q

define the wave speed of a wave

A

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

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15
Q

define the period of a wave

A

the time taken for one wave to pass a point

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16
Q

method for measuring speed of sound waves in air

A

1) person A has cymbals, person B has timer
2) make them stand 500m apart
3) person A crashes cymbals together; person B starts stopwatch when they see person A crash cymbals and stops stopwatch when they hear crash of cymbals
4) calculate speed of sound waves by doing S=D/t

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17
Q

issues with the experiment for measuring speed of sound waves in air and how to resolve them

A
  • different people have different reaction times, giving way for inaccuracies
    to overcome this, we can use a large number of observers with timers and calculating a mean
  • it is only a very short space of time between seeing cymbals crash and hearing them, making it very difficult to press stopwatch at correct times
    increasing distance between the people can reduce this problem
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18
Q

what can waves do between two different materials

A

at the boundary, they can be reflected, absorbed or transmitted

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19
Q

what can sound waves travel through

A

solids, causing vibrations in the solid

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20
Q

how are the limits of human hearing restricted

A

within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound; the conversion of sound waves to vibrations of solids works over a limited frequency range, thus restricting the limits of human hearing

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21
Q

range of normal human hearing

A

20Hz to 20kHz
frequencies outside this range do not cause the ear drum to vibrate

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22
Q

how do microphones detect sound waves

A

the sound waves cause the microphone to vibrate, and microphones transfer these vibrations into an electrical signal by detecting the sound waves’ frequency and amplitude as the waves hit the paper cone, causing it to vibrate forwards and backwards

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23
Q

what do sound waves move faster in and why

A

sound waves move faster in solids than in gases because they are longitudinal mechanical waves rather than being electromagnetic, so because particles are closer together in solids, vibrations can be passed on more easily between them

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24
Q

what happens when waves move from one medium to another

A

their speed can change; when wave speed changes as waves pass from one medium to another, wavelength must also change - that is because the frequency never changes (bc that would mean we’re not abiding by the law of conservation of energy)
therefore increasing wave speed would increase wavelength, and decreasing wave speed would decrease wavelength

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25
Q

what does a cathode ray oscilloscope do and what’s an issue with using one

A

it allows us to see the features of sound waves; the only issue is that it represents sound waves as transverse waves which is incorrect

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26
Q

cathode ray oscilloscope wave property meanings

A
  • frequency controls pitch; high frequency means high pitch and vice versa
  • amplitude controls volume; high amplitude means loud volume and vice versa
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27
Q

define echo

A

a reflected sound wave

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28
Q

what is ultrasound

A

sound waves with a frequency higher than the upper limit of hearing for humans (i.e., >20kHz)

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28
Q

what is ultrasound

A

sound waves with a frequency higher than the upper limit of hearing for humans (i.e., >20kHz)

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29
Q

what happens to ultrasound waves at a boundary

A

they are partially reflected when they meet a boundary between two different media (with different densities)

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30
Q

how can you determine how far away a boundary is

A

use the time taken for the reflections to reach a detector, and multiply it by the speed of the ultrasound wave (which is shown on the device)

this is the distance = speed x time equation

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31
Q

what are ultrasound waves used for

A
  • medical imaging; e.g., internal organs, prenatal scanning
  • industrial imaging; e.g., detecting hidden defects like cracks or air bubbles
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32
Q

condition for using ultrasound waves for producing images of internal organs

A

the organ cannot be surrounded by bone, otherwise it would absorb the ultrasound wave and wouldn’t be detected by the scanner

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33
Q

pros of ultrasound waves over x-rays

A
  • ultrasound is much safer than x-rays because it is non-ionising unlike x-rays, therefore it doesn’t increase the risk of mutations and cancer
  • ultrasound can distinguish between two different types of soft tissue, unlike x-rays which would just penetrate through both
34
Q

why can ultrasound be used for industrial imaging

A

because there is a difference in density between hidden defects like air bubbles and the rest of the material, so partial reflection takes place at the boundary

35
Q

state of the layers of the earth

A

mantle - solid
outer core - liquid
inner core - solid

36
Q

what did the study of seismic waves aid

A

they provided new evidence that led to discoveries about the structure of the Earth which is not directly observable

37
Q

how are seismic waves produced

A

they’re produced by earthquakes; when an earthquake occurs due to a sudden movement between tectonic plates in the earth’s crust, seismic waves are emitted, which carry energy away from the earthquake

38
Q

what happens after seismic waves are emitted

A

they can pass through the earth and be detected by seismometers; the patterns of these waves give us the information about the internal structure of the earth

39
Q

types of seismic waves

A

P-waves (primary waves)
S-waves (secondary waves)

PLease SiT (PLST)
P Longitudinal, S Transverse

40
Q

what type of waves are the seismic waves

A
  • P-waves are longitudinal seismic waves
  • S-waves are transverse seismic waves
41
Q

what can the seismic waves pass through

A
  • P-waves can travel at different speeds through both solids and liquids
  • S-waves can only travel through solids

S- waves Solids (way to remember)

42
Q

what seismic wave travels faster

A

p waves travel faster than s waves

43
Q

define echo sounding

A

the use of high frequency sound waves to detect objects in deep water and measure water depth

44
Q

define electromagnetic waves

A

transverse waves that transfer energy from the source of the waves to an absorber

45
Q

what do electromagnetic waves form

A

they form a continuous spectrum

46
Q

how do electromagnetic waves travel

A

they travel at the same velocity through a vacuum (space) or air

47
Q

how are electromagnetic waves grouped

A

in terms of their wavelength and their frequency

48
Q

order of electromagnetic waves

A

Red - radio waves
Men - microwaves
Invaded - infrared
Venus - visible light
Using - ultraviolet
X-Ray - x-ray
Guns - gamma rays

49
Q

electromagnetic wave spectrum from short to long wavelength

A

gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves

50
Q

electromagnetic wave spectrum from low to high frequency

A

radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays

51
Q

what electromagnetic wave(s) do our eyes detect

A

our eyes only detect visible light and so detect a limited range of electromagnetic waves

52
Q

what are radio waves produced by

A

oscillations in electrical circuits

53
Q

what happens when radio waves are absorbed

A

they may create an alternating current with the same frequency as the radio wave itself, so radio waves can themselves induce oscillations in an electrical current

54
Q

what do gamma rays originate from

A

changes in the nucleus of an atom

55
Q

what do changes in atoms and the nuclei of atoms result in

A

electromagnetic waves being generated or absorbed over a wide frequency range

56
Q

what electromagnetic waves can have hazardous effects

A

ultraviolet waves, x-rays and gamma rays on human body tissue

57
Q

what do the hazardous effects from electromagnetic waves depend on

A

the type of radiation and the size of the dose

58
Q

define radiation dose

A

a measure of the risk of harm resulting from an exposure of the body to the radiation

59
Q

unit of radiation + conversion

A

sieverts (Sv)

1000 millisieverts (mSv) = 1 sievert (Sv)

60
Q

effect of ultraviolet waves on the body

A

they can cause skin to age prematurely and increase the risk of skin cancer

61
Q

effect of x-rays and gamma rays on the body

A

they are ionising radiation that can cause the mutation of genes and cancer

62
Q

practical applications of radio waves and how its suitable

A

television and radio
- they can easily pass through air

63
Q

practical applications of microwaves and how its suitable

A

satellite communications, cooking food
- microwaves are absorbed by water molecules in the food; the energy carried by the waves turns into thermal energy in the food

64
Q

practical applications of infrared waves and how its suitable

A

electrical heaters, cooking food, infrared cameras

65
Q

practical applications of visible light waves and how its suitable

A

fibre optic communications

66
Q

practical applications of ultraviolet waves and how its suitable

A

energy efficient lamps, sun tanning

67
Q

practical applications of x-rays and gamma rays and how its suitable

A

medical imaging and treatments

68
Q

how does a lens form an image

A

by refracting light

69
Q

describe how a convex lens works

A

parallel rays of light are brought to a focus a the principal focus

70
Q

define the focal length

A

the distance from the lens to the principal focus

71
Q

what do ray diagrams show

A

the formation of images by convex and concave lens

72
Q

images produced by convex lens vs concave lens

A

convex lens; can either be real or virtual
concave lens; always virtual

73
Q

define specular reflection

A

reflection from a smooth surface in a single direction

74
Q

define diffuse reflection

A

reflection from a rough surface causes scattering

75
Q

how do colour filters work

A

by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour)

76
Q

how is the colour of an opaque object determined

A

it’s determined by which wavelengths of light are more strongly reflected; wavelengths that are not reflected are absorbed. if all wavelengths are reflected equally the object appears white; if all wavelengths are absorbed the object appears black

77
Q

define transparent or translucent objects

A

objects that transmit light

78
Q

what objects absorb infrared radiation and under what conditions

A

all bodies (objects), no matter what temperature, emit and absorb infrared radiation. the hotter the body, the more infrared radiation it radiates in a given time

79
Q

define a perfect black body

A

an object that absorbs all of the radiation incident on it. a black body does not reflect or transmit any radiation; since a good absorber is also a good emitter, a perfect black body would be the best possible emitter

80
Q

how are changes in velocity, frequency and wavelength are inter-related in the transmission of sound waves

A

velocity of sound is directly proportional to the wavelength, thus, if the velocity of sound doubles when it travels from one medium to another, its wavelength also doubles; the frequency of sound depends upon the source of sound, not the medium of propagation so it does not change.

81
Q

what is the property of a body at constant temperature

A

it is absorbing radiation at the same rate as it is emitting radiation

82
Q

when does the temperature of a body increase

A

when the body absorbs radiation faster than it emits radiation

83
Q

what factors does the temp of the earth depend on

A
  • the rates of absorption and emission of radiation
  • reflection of radiation into space

physics spec (10 decks)

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