Waves Flashcards
(91 cards)
1
Q
what is amplitude?
A
the greatest displacement of a wave, measured from the midpoint
2
Q
what is the wavelength?
A
the length of one oscillation (cycle) of a wave - the distance from a point on one qave to the equivalent point on the adjacent wave
3
Q
what is frequency?
A
the number of oscillations (cycles) of a wave per second, measured in Hertz (1 Hz is one oscillation per second)
4
Q
what is the time period?
A
time for one oscillation (cycle) of a wave
5
Q
how do you calculate period?
A
1 / frequency
6
Q
how do you calculate wave speed?
A
frequency x wavelength
7
Q
what is the rest position?
A
the undisturbed position of particles or fields when they are not vibrating
8
Q
what is displacement?
A
the distance that a certain point in the medium has moved from its rest position
9
Q
what is a peak?
A
the highest point above the rest position
10
Q
what is a trough?
A
the lowest point below the rest position
11
Q
do electromagnetic waves need a medium to travel through?
A
no
12
Q
do mechanical waves need a medium to travel through ?
A
yes
13
Q
are frequency and wavelength directly or inversely proportional ?
A
inversely
14
Q
do transverse waves oscillate perpendicular or parallel to the direction of energy transfer?
A
perpendicular
15
Q
longitudinal waves oscillate perpendicular or parallel to the direction of energy transfer?
A
parallel
16
Q
what are some examples of transverse waves?
A
- light
- all EM waves
- ripples on water
- S waves (seismic)
17
Q
what are some examples of longitudinal waves?
A
- sound
- ultrasound
- pressure waves
- P waves (seismic)
18
Q
what is a compression?
A
Region in a longitudinal wave where the particles are closest together.
19
Q
what is a rarefaction?
A
regions in a longitudinal wave of low pressure due to particles being spread further apart
20
Q
angle of incidence = ?
A
angle of reflection
21
Q
what happens when light passes through an object?
A
some of the light is reflected, some of the light is transmitted, and a small amount may be absorbed
22
Q
what is specular reflection?
A
reflection from a smooth surface which gives a sharp image
23
Q
what is diffuse reflection?
A
reflection from a rough surface - light is scattered in lots of different directions
24
Q
what happens as light passes from air into glass?
A
it moves towards the normal (AOI is greater than AOR)
25
what happens as as light passes from glass into air?
it moves away from the normal (AOI is less than AOR)
26
why does light refract?
due to a change in speed when it enters an optically denser material
27
what is the speed of sound in air?
330 m/s
28
why does sound travel faster in solids and liquids?
because it will be transmitted through the material faster as the particles are much closer together
29
how do ears detect sound?
- Sound waves enter the ear canal and cause the eardrum to vibrate.
- Three small bones transmit these vibrations to the cochlea.
- This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.
30
what is the human hearing range?
20Hz to 20000 Hz
31
what is ultrasound?
sound waves with a frequency over 20kHz or 20,000 Hz
32
why is ultrasound useful?
it is not ionising or heating
33
what is ultrasound used for?
- medical scans
- cleaning medical equipment and jewellery
- finding flaws in metal
34
how can ultrasound be used to detect flaws?
- when ultrasound reaches a boundary between two substances with different densities, they are partly reflected back and the remainder of the waves pass through
- detector placed near source of waves detects the reflected waves
- detector measures the time between a wave leaving the source and reaching the detector - the further the boundary, the longer the time between leaving the source and reaching the detector
- if wave takes less time than usual to reflect back, something must have been in the way to reflect this wave - therefore there is a flaw there
35
describe the structure of the earth
- solid inner core
- liquid outer core
- solid mantle
- solid crust
36
what are the 2 types of seismic waves?
- primary waves (P waves)
- transverse waves (S waves)
37
what are primary waves?
- travel faster
- are detected first
- longitudinal waves
- travel through outer liquid core as can pass through both solids and liquids
38
what are transverse waves?
- travel more slowly
- are detected later
- don't travel through outer liquid core as can only pass through solids
39
how do seismic waves help scientists understand the structure of the earth?
P waves refract at the core and S waves can't be detected on the opposite side of the earth
40
what is the electromagnetic spectrum?
a range of frequencies of electromagnetic waves, ranging in wavelength from 1x10^-4m to 1x10^-15m
41
what types of waves are electromagnetic waves?
transverse (that transfer energy from the source of the waves to an absorber)
42
can EM waves travel through vacuums?
yes
43
do EM waves travel in different speeds through a vacuum or air?
no, they travel at the same speed through a vacuum or the air
44
do all types of electromagnetic waves travel at the same or different velocities through a vacuum?
same - speed of light
45
list the electromagnetic spectrum from long wavelength and low frequency to short wavelength and high frequency
- radio waves
- microwaves
- infrared radiation
- visible light
- ultraviolet light
- x rays
- gamma rays
46
what are the uses and dangers of radio waves?
- communication systems in radio and television
- heating (minimal)
47
what are the uses and dangers of microwaves?
- heating food, satellite communications
- heating
48
what are the uses and dangers of infrared radiation?
- electrical heaters, remote controls, cooking food, infrared cameras
- heating
49
what are the uses and dangers of of visible light?
- seeing
- blinding
50
what are the uses and dangers of ultraviolet light?
- sterilisation, sun tanning, energy efficient lamps
- ionisation
51
what are the uses and dangers of x-rays?
- seeing bones and other medical scans, luggage scans for bombs
- ionisation
52
what are the uses and dangers of gamma rays?
- cancer treatment
- ionisation
53
what properties make radio waves useful for use in radios?
- transmitted easily through air.
- do not cause damage if absorbed by the human body
- can be reflected to change their direction.
54
how are radio waves produced and used?
- by oscillations in electrical circuits.
- When radio waves are absorbed by a conductor, they create an alternating current.
- This electrical current has the same frequency as the radio waves.
- Information is coded into the wave before transmission, which can then be decoded when the wave is received.
55
how do microwaves work?
- High frequency microwaves have frequencies which are easily absorbed by molecules in food.
- The internal energy of the molecules increases when they absorb microwaves, which causes heating.
56
how does infrared radiation cause heating?
- it has frequencies which are absorbed by some chemical bonds
- the internal energy of the bonds increases when they absorb infrared light, which causes heating.
57
how do fibre optic communications work?
coded pulses of light travel through glass fibres from a source to a receiver.
58
how is ultraviolet light used to create energy efficient lamps?
Fluorescent substances absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light.
59
what properties of x rays make them useful for internal imaging?
they are transmitted through body tissues with very little absorption but are absorbed by dense structures like bones
60
what is the wavelength of visible light?
400nm (violet) to 700nm (red)
61
what are primary light colours?
red, green and blue
62
what are the secondary light colours?
cyan, magenta and yellow
63
how do TV screens produce colour?
consist of tiny RGB pixels and varying the brightness of each produces every what we see as every other colour of light
64
how do we observe the colour of an object?
due to the wavelengths of light that it reflects.
65
what primary colours will be reflected and absorbed from a red object?
reflects: red - absorbs: green, blue
66
what primary colours will be reflected and absorbed from a green object?
reflects: green - absorbs: red, blue
67
what primary colours will be reflected and absorbed from a blue object?
reflects: blue - absorbs: red, green
68
what primary colours will be reflected and absorbed from a cyan object?
reflects: green and blue - absorbs: red
69
what primary colours will be reflected and absorbed from a magenta object?
reflects: red and blue - absorbs: green
70
what primary colours will be reflected and absorbed from a yellow object?
reflects: red and green - absorbs: blue
71
what primary colours will be reflected and absorbed from a white object?
reflects: red, blue, green - absorbs: none
72
what primary colours will be reflected and absorbed from a black object?
reflects: none - absorbs: green, red, blue
73
if a red light shines on a red object, what colour will the object appear?
red
74
if a red light shines on a white object, what colour will the object appear?
red
75
if a blue light shines on a red object, what colour will the object appear?
black
76
if a blue light shines on a cyan object, what colour will the object appear?
blue
77
if a green light shines on a magenta object, what colour will the object appear?
black
78
if a yellow light shines on a green object, what colour will the object appear?
green
79
how do filters work?
Filters selectively allow transmission of certain frequencies of while absorbing others.
80
what is a convex lens?
is fatter at the middle and converges light
81
what is a concave lens?
is fatter at the edges and diverges light
82
where are the principle focusses?
on each side of a lens
83
in light ray diagrams, if the image is formed where 2 rays of light meet what kind of image is it?
real
84
in light ray diagrams, if the image is formed from a dashed line because the 2 rays diverge, what kind of image is it?
virtual
85
what are the words used to label images in light ray diagrams?
real or virtual, magnified or diminished, upright or inverted
86
what is the principal focus?
the focal point: where light rays diverge from or converge towards
87
what is a real image?
An image formed when light rays actually meet at a point - can be projected on a screen
88
what is the focal length?
Distance between a focal point and the centre of a lens or mirror.
89
what is a virtual image?
An image formed by the apparent intersection of light rays - cannot be projected on a screen.
90
what is the magnification equation?
Magnification = image size / object size
91
