Waves Flashcards
1
Q
what do all waves do
A
transfer energy from one place to another
2
Q
what is a transverse wave
A
a wave where oscillations are perpendicular to the direction of energy transfer
3
Q
what is a longitudinal wave
A
a wave where oscillations are parallel to the direction of energy transfer
4
Q
what do all longitudinal waves need
A
a medium to travel in
5
Q
example of transverse wave
A
light, electromagnetic wave
6
Q
example of longitudinal waves
A
sound waves
7
Q
features of transverse waves
A
have peaks and troughs
8
Q
features of longitudinal waves
A
have compressions and rarefactions
9
Q
what is important to know about the movement of waves
A
the wave moves and not whatever it passes through
10
Q
what is amplitude
A
maximum displacement of a point on a wave away from its undisturbed position
11
Q
what is wavelength
A
the distance from a point on one wave to the equivalent point on the adjacent wave
12
Q
what is frequency
A
the number of waves passing a point each second
13
Q
what is the unit of waves
A
Hz
14
Q
what is period
A
the time for one wave to pass a point
15
Q
wave speed equation
A
wave speed = frequency x wavelength
16
Q
period equation
A
period = 1/ velocity
17
Q
what is wave speed
A
the speed at which the wave moves through the medium
18
Q
method to measure speed of sound waves in air
A
- one person stands 100m from a large flat wall
- the person claps and another person measures the time taken to hear the echo
- calculate speed using distance x time
- distance is double because the wave has travelled to the wall and back
- repeat to reduce human error
19
Q
what determines how quickly sound waves travel
A
the density of the medium
20
Q
where do sound waves travel fastest
A
a solid as spaces between particles is smaller so vibrations and energy can be passed on more quickly
21
Q
what is the speed of sound in air
A
330m/s
22
Q
Ripple tank practical method
A
- Fill the ripple tank of water to 5mm and place it on top of a piece of white paper
- place a vibrating bar on the surface of the water and attach it to a power pack
- place a lamp above the ripple tank
- turn on the power so the bar vibrates creating waves across the water surface
- to measure wavelength place a metre ruler on paper and use a stroboscope to freeze the wave patterns - measure as many wavefronts as possible and divide by the number of waves
- to measure frequency, place a timer next to the paper and count the number of waves passing a point in 10 seconds
- to calculate wave speed multiply the wavelength by the frequency
23
Q
Waves in a solid practical method
A
- attach a string at one end to a vibration generator, other end to a hanging mass to keep string taut
- attach vibration generator to a signal generator
- produce a standing wave on vibrating string by adjusting the frequency
- to measure wavelength use a metre ruler to measure across multiple standing waves and divide by number of total waves
- to measure frequency use a stopwatch to time wave oscillations over 10 cycles and divide value by 10 to find the time period and put into frequency equation
- to calculate wave speed multiply wavelength by frequency
24
Q
safety precautions of wave practicals
A
take care working with water and electricity - mop up spillages
don’t stand beneath masses in case weights fall off
wear safety goggles when using oscillating string as it may snap at high frequency
25
what changes in sound waves when they move from one medium to another
wave speed
frequency
wavelength
26
where do sound waves travel slowest
gasrd
27
how do sound waves transfer energy
by the molecules vibrating and knocking into neighbouring particles
28
how is the relationship between wave speed , wavelength and frequency determined
using wave speed = frequency x wavelength
29
what can the change in velocity of a sound wave result in
a change of direction of the sound wave (refraction)
30
what happens when sound moves from a denser medium to a less dense medium
the wavelength of the sound wave decreases
the frequency of the sound wave stays the same
the velocity of the sound wave decreases
31
what happens when sound waves move from a less dense medium to a denser medium
the wavelength of the sound wave increases
the frequency of the sound wave stays the same
the velocity of the sound wave also increases
32
what is the speed of sound in air affected by
temperature
33
what happens to the speed of sound on warm days
air molecules move faster so they carry sound waves faster increasing speed of sound
34
what happens to the speed of sound on cold days
air molecules move at a slower pace so they carry sound waves at a slower pace decreasing the speed of sound
35
what happens as frequency of a wave increases
velocity increases
36
what happens as wavelength increases
velocity increases
37
what is period inversely proportional to
frequency
38
what does a smaller wave period mean
higher frequency, greater velocity
39
what can happen to waves at the boundary between two materials
reflected
absorbed
transmitted
40
features of reflection of waves
-waves will reflect off a flat surface
-the smoother the surface, the stronger the reflected wave is
-rough surfaces scatter the light in all directions so they appear matt and not reflective
-the angle of incidence = angle of reflection
-light will reflect if the object is opaque and is not absorbed by the material as the electrons will absorb the light energy and remit it as a reflected wave
41
features of transmission of waves
- waves will pass through a transparent material
-the more transparent the more light will pass through the material
-it can still refract but the process of passing through the material and still emerging is transmission
42
features of absorption of waves
-if the frequency of light matches the energy levels of the electrons
the light will be absorbed by the electrons and not re-emitted
they will be absorbed and then re-emitted over time as heat
so that particular frequency has been absorbed
if a material appears green, only green light has been reflected ad the rest of the frequencies in visible light have been absorbed
43
what happens when sound waves travel through solids
they cause vibrations in the solid
44
how does the body collect sound
the outer ear collects the sound and channels it down the ear canal
45
what kind of wave is a sound wave as it travels down the ear canal
it is still a pressure air wave
46
what happens when the sound waves hit the eardrum
tightly stretched membrane vibrate as the incoming pressure waves reach it making
compression forces the eardrum inward
rarefaction forces the eardrum outward due to pressure
so the eardrum vibrates at the same frequency as the sound wave
the small bones connected to this also vibrate at the same time (stirrup bone)
47
where is the vibrations in the bones from a sound wave transmitted to
the fluid in the inner ear
48
where are compression waves transferred to in the ear
the fluid in the cochlea
49
what happens as the fluid moves in the ear
the small bones act as an amplifier of the sound waves
as the fluid moves due to the compression waves, the small hairs that line the cochlea move too
each hair from nerve cells is sensitive to different sound frequencies so some move more than others for certain frequencies
when a certain frequency is received the hair attuned to that frequency moves a lot releasing an electrical impulse to the brain which is interpreted as a sound
50
what is human hearing range
20Hz to 20kHz
51
what can happen in the ear that affects human hearing
in the cochlea the hairs attuned to higher frequencies die or get damaged
52
what are causes of hairs attuned to higher frequencies dying or becoming damaged
constant loud noise damaging the hairs over the years
changes in the inner ear as growing older
smoking, chemotherapy, diabetes
53
why have humans evolved to hear this range of frequencies
it gives the greatest survival advantage
54
why can humans not hear ultrasound
we do not use sonar to hunt , we have accurate vision instead of
55
what happens when ultrasound reaches a boundary between two media
they are partially reflected back
56
what happens to the remainder of the waves that are not reflected back in ultrasound
they continue and pass through so a receiver next to the emitter can record the reflected waves
57
how does the receiver show the distance from the source the waves are
the speed of the waves are constant so measuring the time between emission and detection can show distance
58
how can ultrasound be used for imaging under surfaces
a crack in a metal block will cause some waves to reflect earlier than the rest so will show up
59
what is infrasound/ seismic waves
a sound wave with a frequency lower than 20Hz
60
what are the two seismic waves
P and S waves
61
features of P waves
longitudinal and can pass through solids and liquids
62
features of S waves
transverse and only pass through solids , slower than P waves, bent by changing density of a rock
63
features of an L wave
arrive last and cause vigorous movement on the surface
travel more slowly than P waves and S waves
64
why do p and s wave bend towards the surface of the earth as they travel through the earth
their speed and direction changes at different densities (refraction)
65
why do seismic waves prove the structure of the earths core
there is a liquid core under the mantle because S waves do not travel through the outer core as they cannot travel through liquid
66
what is echo sounding
using high frequency sound waves
67
what is echo sounding used for
detecting objects in deep water such as shoal of fish
or detecting how far the seabed is below the ship
68
how does echo sounding work
pule of ultrasound is sent below a ship and the time taken for it to reflect and reach the ship is used to calculate the depth
69
what are electromagnetic waves
transverse waves that transfer energy from the source of the waves to an absorber
70
what do electromagnetic waves form
a continuous spectrum
71
features of electromagnetic waves
do not need particles to move
in space they all have the same velocity (speed of light)
can transfer energy from a source to an absorber
transverse waves
72
examples of electromagnetic waves transferring energy from a source to an absorber
microwave source to food
sun emits energy to earth
73
how are the waves grouped in the electromagnetic spectrum
long to short wavelength
low to high frequency
74
electromagnetic spectrum order
radio waves
microwaves
infrared
visible light
ultraviolet
x rays
gamma rays
75
why do our eyes only detect a limited range of electromagnetic waves
they can only detect visible light
76
what does speed being constant for all EM waves result in
as wavelength decreases, frequency must increase
as frequency increases , energy of the wave increases
77
what happens to refraction entering a denser material
it bends towards the normal
78
what happens to refraction if entering a less dense material
it bends away from the normal
79
what will substances do with EM waves depending on wavelength
absorb
transmit
refract
reflect
80
glass reacting to em waves
transmit/ refract visible light
absorb uv radiation
reflect ir radiation
81
why do material interact differently for different parts of the EM spectrum
the wavelengths and frequencies are different
82
what are some effects on objects from the EM spectrum due to
differences in velocity
83
why are some effects due to differences in velocity
when light enters a denser medium it slows down
shorter wavelengths slow down more than longer wavelengths
84
why does dispersion occur of white light into a prism
the different wavelengths refract to a different amount therefore spread put creating a rainbow effect
85
what happens when refracting
the speed decreases and wavelength decreases too in denser materials
86
how are radio waves produced
oscillations in electrical circuits
87
what happens when radio waves are absorbed
they create an alternating current at the same frequency as the radio waves
88
what happens when electrons move to a higher orbit (further from nucleus)
the atom has absorbed em radiation
89
what happens when electrons fall to a lower orbit (closer tot he nucleus
the atom has emitted em radiation
90
what happens if an electron gains enough energy
it can leave the atom to form an ion
91
what do gamma rays originate from
changes in the nucleus of an atom
92
which em waves can have hazardous effects on human body tissue
uv light
x rays
gamma
93
what does the effect of harmful em waves on the body depend on
the type of radiation and the size of the dose
94
what does radiation dose mean
the risk of harm resulting from an exposure of the body to radiation
95
how does uv radiation harm humans
skin ages prematurely increasing risk of skin cancer
96
how is damage from uv radiation prevented
suncream prevents overexposure
97
how does x ray and gamma ray harm humans
ionising radiation so can cause mutation of genes which causes cancer
98
how is harm from x rays and gamma rays prevented
minimal exposure should be ensured
99
what are radio waves used for
TV and radio
100
why are radio waves used for TV and radio
long wavelength, can travel far without losing quality
101
what are microwaves used for
satellite communication
cooking food
102
why are microwaves used for satellite communication and cooking food
can penetrate the atmosphere to reach satellites
103
what ir IR radiation used for
cooking food
infrared cameras
104
why is ir radiation used to cook food and for ir cameras
transfers thermal energy
105
what is visible light used for
fibre optics
106
why is visible light used for fibre optics
best reflection/ scattering in glass (others have too short/long wavelengths)
107
what is uv light used for
sun tanning
energy efficient lamps
108
why is uv used for sun tanning and energy efficienct lamps
radiates the least heat but more energy
109
what is x ray and gamma ray used for
medical imaging and treatment
110
why is x ray and gamma ray used for medical imaging and treatment
very high in energy and can penetrate material easily
111
what happens if light passes through the centre of a lens
it does not change direction
112
what are focal points
points either side of the lens which light can converge at
113
what can convex lenses have
virtual or real images
114
what images to concave lenses have
virtual images
115
features of a concave lens
caves inward
thinner at the centre than edges
spreads light outwards
light appears to have come from the focal point of
116
what do concave lenses do
spread out light further
117
what are concave lenses used for
correct short sightedness
as light is focused on the front of the retina so needs to be spread out slightly to be able to be focused onto the retina
118
features of convex lenses
wider at the centre
focus light inwards
horizontal rays focus onto focal point
119
what are convex lenses used for
magnifying glasses]
binoculars
correct long sightedness
120
what do convex lenses do
focuses the rays closer
121
magnification equation
image height / object height
122
law of reflection
for a plane mirror the angle of incident is equal to the angle of reflection
123
what does each colour within visible light spectrum have
its own narrow band of wavelength and frequency
124
difference between blue and red
blue has a shorter wavelength and higher frequency than red
125
what is sunlight in terms of its composition
a mix of all colours and this mix appears white (white light is normal light)
126
types of reflection
specular
diffuse
127
what is specular reflection
smooth surface gives a single reflection
128
what is diffuse reflection
reflection off a rough surface causes scattering
129
how do colour filters work
the filter absorbs every other colour and only lets a certain wavelength (colour) through
130
what does an opaque object have
colour
131
what is an opaque objects colour determined by
the strength of reflection for different wavelengths
132
what happens to wavelengths that are not reflected
they are absorbed
133
what happens if all wavelengths reflect
it is white in colour
134
what happens if all wavelengths are absorbed
it appears black
135
what does the wavelength absorbed equal
the colour which it appears
136
what are objects that transmit light
either transparent or translucent (scatter most light and on;y let some through)
137
what do all objects do
emit and absorb infrared radiation
138
what happens the hotter the body
the greater amount for radiation released per second (more powerful)
the greater amount of shorter wavelength radiation released (waves with more energy like x rays)
139
what is a black body
an object that absorbs all the radiation it receives and doesn't transmit or reflect any
therefore it emits all types of radiation
140
what does a body do at its constant temperare
it is still radiating / receiving radiation
but it is absorbing radiation at the same rate of emitting it
141
what does a body do at an increasing temperature
absorbs more energy than it emits
142
what does a body do when cooling down
energy is released at a greater rate than it absorbs
143
what is the suns energy mostly absorbed by
the earths atmosphere , and some is reflected
144
what does the amount for energy re radiated and absorbed lead to
the earths temperature
145
process of the earth receiving solar radiation
solar radiation passes through the atmosphere
some solar radiation is reflected by the atmosphere and earths surface
about half is absorbed by earths surface
radiation converted to heat energy causing emission of ir radiation back into the atmosphere
some of the ir radiation is absorbed and reemitted by greenhouse gas molecules
some ir radiation passes through the atmosphere and into space
