Physics all of waves Flashcards
(118 cards)
1
Q
What do waves transfer ?
A
Waves transfer energy from one place to another without transferring matter.
2
Q
How can wave motion be shown ?
A
Wave motion is the movement of waves can be shown by the vibrations of a spring or by water waves
3
Q
What type of wave is demonstrated when one end of a spring is moved up and down while the other end is fixed ?
A
Transverse wave
4
Q
What happens to a cork floating on the surface of water when a wave passes ?
A
The cork moves up and down but does not travel with the wave
5
Q
How do waves affect floating objects like a cork ?
A
Floating objects experience vertical displacement only, they do not move forward with the wave
6
Q
What do waves transfer ?
A
Waves transfer energy
7
Q
What do all waves have ?
A
All waves have a frequency and a period of oscillation
8
Q
What is Frequency ?
A
Frequency is the number of oscillations (vibrations) per secound
9
Q
What is the meaning of periodic time ?
A
The periodic time of a wave is the time taken to complete one oscillation ( vibration)
10
Q
What is the frequency equal to ?
A
It is equal to 1 divided by the period
11
Q
What is Frequency measured in ?
A
Frequency is measured in Hertz (Hz)
12
Q
How do you calculate the periodic time ?
A
Periodic time = 1 / frequency
13
Q
What is the periodic time of a wave measured in ?
A
It is measured in secounds
14
Q
What unit is the periodic time of a wave measured in ?
A
seconds
15
Q
What is the meaning of amplitude of a wave ?
A
The amplitude of a wave is the largest distance that a point on the wave moves from its rest position
16
Q
What is the meaning of wavelength ?
A
The wavelength is the distance between two adjacent wave fronts.
17
Q
What is defined as the greatest distance a point on the wave moves from its rest position?
A
Amplitude
18
Q
What is the equation for frequency of a wave
A
Wave frequency = Number of oscillations/ time
19
Q
What is the formula for wave speed ?
A
Wave speed = frequency x wavelength
20
Q
What are the elements of the wave speed equation ?
A
Wave speed
Frequency
Wavelength
21
Q
What is the formula for wave speed ?
A
Wave speed = Frequency x wavelength
22
Q
What does phase of a wave mean ?
A
It describes how far through a cycle the wave is.
23
Q
What is phase difference ?
A
Phase difference is a measure of the difference in where two waves are in their cycle
24
Q
What angles be measured in ?
A
Angles can be measured in degrees or radians
25
What can phase difference be measured in ?
Phase difference can be measured in angles or as a fraction of the wave cycle or multiple of wavelengths
26
How many radians are in 180 degrees ?
Pi
27
In what position do particles end up after a transverse wave has passed?
Same position
28
What are examples of longitudinal waves ?
P-waves
Sound
29
What are examples of transverse waves ?
Water waves
Mexican wave
Electromagnetic spectrum
30
What do electromagnetic waves travel ?
They travel at the speed of light
31
In what direction do the particles move relative to the direction of a longitudinal wave?
Same direction
32
What is a stationary wave ? and how is it formed ?
A stationary wave is formed when two progressive waves each with the same frequency and wavelength and moving in opposite directions , interfere with one Another.
33
What do stationary waves do ?
This creates a wave which does not transfer energy from one place to another.
34
What are Nodes ?
Nodes are Points on a stationary wave that have zero amplitude.
35
What does having zero amplitude mean ?
Zero amplitude means that they are stationary
36
What are antinodes ?
They are points on a stationary wave with maximum amplitude.
37
What do antinodes do ?
They oscillate from the furthest point upwards to the furthest point downwards.
38
When can stationary waves only happen ?
Stationary waves can only happen at resonant frequencies
39
When do resonant frequencies happen ?
It happens when the distance between the two fixed ends is an integer multiple of half wavelengths
40
What is the name of the first resonant frequency ?
It is called the first harmonic
41
When does the first harmonic happen ?
It happens when the distance between the two fixed ends is exactly 1/2
42
What are the features of a first harmonic ?
It has 2 nodes and 1 antinode
The first harmonic is also known as the fundamental
43
What is the secound resonant frequency called ?
The secound harmonic
44
When does the secound harmonic happen ?
It happens when the distance between the two fixed ends is exactly wavelength. It contains two 1/2 wavelengths
45
What are features of the secound harmonic ?
It has a frequency twice as big as the first harmonic.
It has 3 nodes and 2 antinodes
46
What is the third resonant frequency called ?
It is called the third harmonic.
47
When does the third harmonic happen ?
It happen when the distance between the two fixed ends is exactly 1 1/2 wavelength . It contain 3 1/2 wavelengths
48
What are features of the third harmonic ?
It has a frequency three times as big as the first harmonic . It has four nodes and 3 antinodes
49
When can stationary waves only occur ?
Standing waves can only occur at resonant frequencies.
50
What are points on a stationary wave that have zero amplitude calle
Node
51
What does the stationary wave practical investigate ?
It investigates how the frequency of stationary waves on a string changes when length , tension ands mass per unit length are changed
52
What is the full method for stationary wave practical ?
Set up equipment , Vibration generator and mass block
Measure the length of the string, the tension in the string and the mass per unit length.
The tension can be calculated by multiplying the total mass of the mases and the acceleration due to gravity.
The mass per unit length can be calculated by dividing the total mass of the string by its length
Determine the frequency of the first harmonic . This can be found by varying the frequency until you see the pattern needed for the first harmonic. Two nodes at each end of the string with one antinode in the centre.
To investigate how changing the length affects the resonant frequency , keep the tension and mass per unit length the same. Vary the length of the string by moving the oscillator away or towards the pulley
At each string length , find the new first harmonic
Plot a graph of f against l
53
How do you find the mass per unit length of the string ?
Divide the mass by the length
54
In the stationary wave of a string practical, what is the relationship between mass per unit length of string and frequency and why?
The larger the mass per unit length, μ, the lower the resonant frequency.
For the same length string, waves travel more slowly through a heavier string, so the frequency must be lower.
55
What does the pattern of the first harmonic of a stationary wave look like?
One antinode and two modes
56
How many antinodes does the first harmonic have?
One
57
How are stationary waves formed ?
A stationary wave is formed when two progressive waves each with the same frequency and wavelength and moving in opposite directions interfere with one another. This creates a wave which does not transfer energy from one place to another.
58
Which feature of standing waves is created at the point where a guitar string is pressed down on a fret?
A node
59
How does this change the frequency of the vibration compared to plucking the open string?
Increases
60
How does this change the pitch of the guitar string?
Increases
61
How does pressing a guitar string onto a fret affect stationary waves ?
The vibration of guitar strings can be modelled as stationary waves, with nodes at the fixed points of the strings.
To change the frequency of the harmonics of the string and thus the pitch of the note being played, the string is held down onto a fret. This creates a node at one end of the string.
As compared to plucking the open string, the wavelength of the fretted standing wave is reduced, increasing the frequency and pitch of the note played.
62
Which physical quantity is increased by increasing the thickness of the guitar string ?
Mass per unit length
63
How does the thickness of a guitar string affect its sound
Thicker guitar string means lower pitch
64
What is the medium of the sound waves produced by a guitar string?
Air
65
Which feature of a guitar amplifies the sound ?
Soundhole
66
When does interference happen ?
It happens when any two waves are superimposed on one another.
67
What does coherence create ?
It creates a very messy wave pattern
68
What do you need to do to see a clear interference pattern ?
We need two waves that are coherent
69
What does coherent mean ?
It means that the two waves must have the same frequency and wavelength and have a fixed phase relation.
70
What is the fixed phase relation ?
it is zero
71
What is the meaning of path difference ?
It is difference in length traveled by the waves to get to a certain point.
72
When will destructive interference occur ?
Destructive interference will occur when the path difference is equal to an odd number of half wavelengths.
73
What are the conditions for interference ?
The waves must be coherent and monochromatic
Waves must have a path difference of
n
λ
nλ for constructive interference
Waves must have a path difference of
(
n
+
1
/
2
)
λ
(n+1/2)λ for destructive interference
74
What are the conditions for interference?
The light should have the same wavelength
The light should have a fixed phase difference
75
Why do we only use one source for Young's double slit experiment?
So the light is coherent
76
What is laser light ?
Monochromatic and coherent
77
What does Monochromatic mean ?
It means that the light is all the same wavelength
78
What does coherent mean ?
It means that light is in phase and has the same frequency
79
When will we see a diffraction pattern ?
If the wavelength of the laser light is roughly the same as the width of the single slit
80
What do you see in the image of the laser diffraction pattern ?
The image shows the pattern we expect to see in a successful single slit diffraction equipment.
We see a bright central fringe with alternating dark and bright fringes each side
81
What are the bright fringes caused by?
Constructutive interference
82
What are the dark fringes caused by ?
Destructive interference.
83
What happens if you use white light instead of laser light for diffraction grating ?
We see a different but similar diffraction pattern. White light is made up of all the visible colours of light . Each colour is diffracted by different amounts. Red has the longest wavelength so is diffracted the most and appears on the outside of the fringes. Blue has the shortest wavelength so is diffracted the least and appears on the inside of the fringes.
84
In the single slit diffraction experiment, what effect does decreasing the wavelength of incoming light have on the width of the central maximum?
Decreases
85
What is diffraction used to determine in crystals ?
Atomic spacing
86
What is refraction ?
Light changes speed and bends when it passes from one medium to the next.
87
What is the speed of light in a vacuum ( empty space)
3x108 m/s
88
Where does light travel more slowly ?
In all other materials
89
What is the refractive index of a material ?
It is the ratio of the speed of light in a vacuum to the speed of light in that material.
90
What does air contain a lot of ? and give examples
Air contains lots of chemicals and elements such as oxygen and nitrogen
91
What is the refractive index of air approximately ?
1
92
What is total internal reflection ?
At angles of incidence larger than or equal to the critical angle , no light is refracted. Instead all light is reflected.
93
What is the name of the angle at which an incident ray of light is totally reflected ?
Critical angle
94
What are the properties of refraction ?
If light passes into a less dense medium it travels faster.
If light passes into a more dense medium it bends towards the normal.
The larger the refractive index the denser a material is.
95
What is internal reflection and total internal reflection ?
Light speeds up when entering a less optically dense medium. When this happens, some light is refracted and some light is reflected. This is internal reflection.
If the angle of incidence is the same as the critical angle, light will travel along the boundary of the mediums.
If the angle of incidence exceeds the critical angle, then all the light will be reflected. This is called total internal reflection.
96
What is the phenomenon that occurs when light is incident at an angle greater than the critical angle of the boundary between two mediums?
Total internal reflection
97
How do optical fibres transmit light ?
Total internal reflection
98
What are the 3 features of Optical fibres ?
Long distance
Small critical angle
Cladding
99
Why do optical fibres need long distance ?
Most of the light will be totally internally reflected and continue to travel through the core.
100
Why are small critical angles good for optical fibres ?
only light approaching the boundary at an angle that is very close to the normal will cross the boundary and be refracted
101
Why is cladding good for optical fibres ?
Each fibre has a core of optically dense material that is covered by a layer of cladding with a much lower optical density.
This means that the boundary between the two materials has a very small critical angle.
102
What are the key features of an optic fibre? (3)
Core
Cladding
protective coating
103
What is an endoscope ?
Bundles of fibres can be used to transmit an image without a lens
104
What are endoscopes used for ?
To explore the body by insertion through the mouth, nose , small cuts
105
What is the medical use of endoscopes and how does it work ?
Light is transmitted down one fibre bundle to illuminate internal parts and the reflected light is transmitted back out through another to be observed.
Surgery can be performed by attaching cutting tools to an endoscope.
Internal bleeding can also be stopped by using the light from the endoscope to cauterize a bleed.
106
Why do internet providers use optical fibres ?
They transmit lots of information with little information loss.
107
How can surgery be performed with endoscopy ?
By attaching cutting tools to the end of the fibres
108
What are the 2 main benefits of using optic fibres in communications ?
low information losses
Data can travel long distances
109
How many types of waves are there in the electromagnetic spectrum ?
7
110
What are the electromagnetic waves in the electromagnetic spectrum in order of highest frequency to lowest frequency ?
Gamma
x-ray
ultraviolet
visible
infrared
microwave
radio waves
111
What type of electromagnetic wave has the lowest frequency ?
Radio waves
112
What are the uses of gamma rays ?
Medical imaging and therapy
Astronomy
sterilisation
Food preservation
113
What are the risk of gamma rays (Disadvantages)
Extremely penetrating
Damaging to living tissues and cells.
114
What do gamma rays carry ?
They carry out the most energy
115
What can we use gamma rays to do ? ( 1)
Destroy bacteria and tumours
116
What are the risks of x-rays ?
Highly ionising . This means can damage body cells even in low doses.
117
What can x - rays penetrate through ?
soft materials like body tissue
118
