Waves Flashcards
1
Q
How is a wave produced?
A
A wave is produced by a disturbance/ vibration/oscillation which transfers energy and information.
2
Q
wavelength (lambda) (m)
A
The distance between any 2 consecutive waves (eg: 2 consecutive crests or troughs)
3
Q
Transverse
A
It is produced when the disturbance/ vibration is perpendicular (90 degrees) to the direction of energy transfer.
4
Q
examples of transverse waves
A
Electromagetic waves, S-waves secondary seismic waves (earthquakes), ripples on the surface of water, electromagnetic waves (such as radio, light, X-rays etc).
5
Q
longitudinal wave
A
It is produced when the disturbance/ vibration is parallel to the direction of energy/ data transfer
6
Q
Examples of longitudinal waves
A
(P) Primary seismic waves, SOUND waves, pressuure waves caused by repeated movements in a liquid or gas
7
Q
ampLitude (A)
A
The distance from the rest/ median/ equilibrium/ 0 line to the crest or trough. unit= metres
8
Q
What does ampLitude indicate?
A
Loudness
9
Q
FrequenCy
A
It is the number of complete waves that pass a point in a second (unit -Hertz, Hz).
10
Q
What does frequenCy determine?
A
The pitch
11
Q
Period
A
It is the time taken for one complete wave to pass a point (unit- second)
12
Q
Wavespeed (v)
A
frequency (Hz) x wavelength (m). It is the product of frequency (Hz) and wavelength (m)
13
Q
Frequency =
A
1/time period (s)
14
Q
EleCtromAgneTic waves
A
An electromagnetic wave is generated or produced when a Charged particle Accelerates. When a charged particle accelerates, the electric field and magnetic field change.
15
Q
Electromagnetic spectrum (Real Men In Love Usually C-ray Girls)
A
Radio Micro Infrared Visible light Ultraviolet X-ray gamma ray
16
Q
As you go down the electromagnetic spectrum, what happens to wavelength and frequency?
A
The wavelength decreases and the frequency increases.
17
Q
Describe the electromagneTic spectrum
A
Electromagnetic radiation travel as transverse waves and transfers energy from one place to another. All electromagnetic waves can travel through a vacuum- the speed of light. The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in each part of the spectrum have different uses and danger which depend on their wavelengths and frequency.
18
Q
Properties of electromagnetic waves
A
- They are transverse in nature
- They can be reflected and refracted
- They all travel at the same speed in a vacuum (3x 10^8)
- They transfer energy
- Polarisation (cuts out the glare)
19
Q
Sound waves
A
They are longitudinal. They travel as vibrations. They are made up of compressions and rarefactions and are detected by our ear drums. These vibrations are converted to electrical signals in the cochela. Sound can travel through solids, liquids and gases but they cannot travel through vacuums. This is because a vacuum has no particles to vibrate.
20
Q
Properties of transverse waves:
A
- the energy transfer is in the same direction as the wave motion
- They transfer energy, but not the particles of the medium
- Transverse waves can move in a liquid or solid, but not a gas
- Some transverse waves (electromagnetic waves) can move in a vacuum.
21
Q
The point on the wave that is highest above the rest position is called the
A
peak or crest
22
Q
The lowest below the rest position is called what?
A
the trough
23
Q
What are waves?
A
Repeated vibrations that transfer energy. Energy is transferred by parts of the wave knocking nearby parts.
24
Q
Representing transverse waves
A
- They are drawn as a single, continuous line, usually with a central line showing the undisturbed position
- The curves are drawn so that they are perpendicular to the direction of energy transfer
25
Properties of longitudinal waves
- The energy transfer is in the same direction as the wave motion
- they transfer energy but not the particles of the medium
- they can move in solids, liquids and gases
- They can not move in a vacuum (since there are no particles).
26
The key features of a longitudinal wave are where the points are
- close together, called compressions
| - spaced apart, called rarefactions
27
What type of waves can be seen in a slinky spring?
Longitudinal waves when it is moved quickly backwards and forwards.
28
Representing longitudinal waves
- they are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer
- drawing the lines closer together represents the compressions
- drawing the lines further apart represents the rarefactions
29
How can transverse waves be shown on ropes?
The waves travel perpendicular to the vibration of the rope
30
How can longitudinal waves be shown in the vibration of coils?
The waves travel parallel to the vibration of coils.
31
Transverse waves vs Longitudinal waves
- structure: Transverse- peaks and troughs, longitudinal- compressions and rarefactions
- vibration: transverse-90 degrees to direction of energy transfer. Parallel to direction of energy transfer.
- vacuum: transverse- only electromagnetic waves can travel in vacuum, longitudinal waves cannot travel in a vacuum
- Material: tranverse waves- can move in liquids and solids, but not gases. Longitudinal waves- can move in gas, liquids and solids
- density: transverse waves- constant density, longitudinal waves- changes in pressure
- speed of wave: transverse waves- dependant on material it is travelling in, longitudinal waves: dependant on material it is travelling in.
32
wavefronts
- both transverse and longitudinal waves can be represented as wavefronts: this is where the waves are viewed from above
- For a transverse wave: one line represents either a peak or a trough.
- For a longitudinal wave: one line represents either a compression or a rarefaction
- The arrow shows the direction the wave is moving and is sometimes called a ray
- The space between the lines represents the wavelength : - when the lines are close together , this is a wave with a short wavelength.When the lines are far apart, this is a wave with a long wavelength.
33
Q: How does a toy duck demonstrate that waves do not transfer matter
- The type of wave on the surface of a body of water is a transverse wave
- This is because the duck is moving perpendicular to the direction of the wave
- The plastic duck moves up and down but does not travel with the wave
- both transverse and longitudinal waves transfer energy, but not the particles of the medium
- This means when a wave travels between two points, no matter actually travels with it, the points on the wave just vibrate back and forth about fixed positions
- Objects floating on the water simply bob up and down when waves pass under them, demonstrating that there is no movement of matter in the direction of the wave, only energy.
34
In a transverse wave, the wavelength can be measured from
one peak to the next peak
35
In a longitudinal wave, the wavelength can be measured from
the centre of one compression to the centre of the next
36
The distance along a wave is typically put on the
x-axis of a wave diagram
37
Wavespeed definition
The distance travelled by a wave each second
38
Measuring the speed of waves- measuring sound between two points
1, Two people stand a distance of around 100m apart
2, The distance between them is measured using a trundle wheel
3, One person has two wooden blocks, which they bang together above their head
4, The second person has a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound
5, This is then repeated several times and an average value is taken for the time
6, The speed of sound can be calculated using the equation: speed of sound = distance travelled by sound/time taken.
39
measuring the speed of waves - using echoes
1, A person stands 50 m away from a wall (or cliff) using a trundle wheel to measure this distance
2, The person claps two wooden blocks together and listens for the echo
3, The person then starts to clap the blocks together repeatedly, in rhythm with the echoes
4, A second person has a stopwatch and starts timing when they hear one of the claps and stops timing 20 claps later
5, The process if then repeated and an average time calculated
6, The distance travelled by the sound between each clap and echo will be (2x50 m)
7, The total distance travelled by sound during the 20 claps will be (20 x 2 x 50) m
8, The speed of sound can be calculated from this distance and time using the equation:
speed of sound = ( 2 x distance to the wall)/ time taken
40
Measuring the speed of waves- using an oscilloscope
1, Two microphones are connected to an oscilloscope and placed about 5m apart using a tape measure to measure the distance
2, The oscilliscope is set up so that it triggers when the first microphone detects a sound, and the time base id adjusted so that the sound arriving at both microphones can be seen on the screen
3, Two wooden blocks are used to make a large clap next to the first microphone
4, The oscilliscope is then used to determine
41
How do you visualise a transverse wave?- slinky
One student holds the end of the slinky stationary. The other end of the slinky is moved from side to side. A series of pulses moves down the slinky, sending energy from one end to another. The student holding the slinky still feels the energy as it arrives. None of the material in the slinky has moved permanently. The transverse waves transfer energy along the slinky from one end to the other.
42
Water waves and light waves are two examples of
transverse wave
43
Water wave
Energy is carried outwards by the wave, but water does not pile up at the edge of the pond.
44
Longitudinal waves- slinky
Energy is transmitted along the slinky by pulling and pushing the slinky backwards and forwards. This makes the slinky vibrate backwards and forwards. The vibration of the slinky is parallel to the direction of energy transfer. The coils are pushed together in some places (areas of compression). In other places the coils are pulled apart (areas of rarefaction). As energy is transferred, none of the material of the slinky moves permanently.
45
Sound - guitar string
Sound - longitudinal
When a guitar string is plucked, energy is transferred through the air as the string vibrates backwards and forwards. However, the air itself does not move away from the string with the wave- there is not a vacuum left near the guitar.
46
Earthquakes produce
chock waves, which may be either longitudinal or transverse waves.
47
Why are buildings damaged in earthquakes?
They are damaged by the transfer of energy, not by the movement of material
48
Looking at water waves in a ripple tank (to learn more about the properties of waves)
- We can produce waves by lowering a dipper into the tank. A wooden bar is used to produce straight waves (plane waves) and a spherical dipper produces circular waves. By shining a light from above, we see the pattern of waves produced by the peaks and troughs of the waves. Vibrated up and down by motor, glass-bottomed tank, dipper for circular waves, lamp, dipper for straight waves, wave pattern seen on screen.
49
period, T
The time taken to produce one wave
50
time period
1/ frequency
51
wavespeed
The speed at which energy is transferred through the medium.
52
wavespeed (m/s) =
frequency (Hz) x wavelength (m)
| F x lambda
53
Speed of sound in air
340 m/s
54
Measuring the speed of sound in a laboratiory
1, speed = distance travelled/time taken
2, Problem: Sound travels quickly so we must find a way to measure short times accurately in the laboratory.
3, A loudspeaker is connected to a signal generator which produces short pulses of sound.
4, Two microphones are placed near the loudspeaker but separated by a short distance, d. Each microphone is connected to an input of a dual beam oscilloscope.
5, The oscilloscope can measure the time difference, t, between the sound reaching microphone A and microphone B.
55
Measuring the speed of sound outside
- When outside, the echoes from a tall building can be used to measure the speed of sound in air
- Stand 40 m in front of a tall building and bang two blocks of wood together
- Each time you hear an echo, bang the blocks together again
- Have another student use a stopwatch to time how long it took to hear a fixed number of/10 echoes.
- Format your results in a table.
- Calculate the mean value of the time for 10 echoes
- Calculate the speed of sound given by these results
56
Investigating waves in a ripple tank
1, Set up the ripple tank as shown
2, Pour enough water to fill the tank to a depth of about 5 or 6 mm
3, Adjust the wooden bar up or down so that it just touches the surface of the water
4, Switch on the lamp and the electric motor.
5, Adjust the speed of the motor so that low frequency waves that can be counted are produced
6, Move the lamp up or down so that a clear pattern can be seen on the floor
7, If the pattern is dfficult to see, a sheet of white paper or card on the floor under the tank and the laboratory lights may help.
8, Use a metre ruler to measure across as many waves in the pattern as possible. Divide that length by the number of waves. This gives the wavelength of the waves.
9, Count the number of waves passing a point in the pattern over a given time (eg: 10 seconds). Divide the number of waves counted by 10. This gives the frequency of the waves. If you have connected the motor to a variable frequency power supply you can take the frequency directly from the power supply.
EQUIPMENT: wave pattern seen on screen, glass-bottomed tank, dipper for circular waves, vibrated up and down by motor, dipper for straight waves, lamp
Use wavespeed = frequency x wavelength to calculate wave speed
57
Waves in a stretched spring
- You can either use a string or elastic cord for this investigation
- to power supply, string, vibration generator, wooden bridge, pulley, masses
1, Switch on the vibration generator. The string (or elastic cord) will start to vibrate but not in any pattern.
2, Changing the mass attached to the string changes the tension in the string. Moving the wooden bridge changes the length of the string that vibrates.
3, Change the mass or move the wooden bridge until you see a clear wave pattern. The pattern will look like a series of loops. The length of each loop is half a wavelength.
4, Use a metre ruler to measure across as many loops as possible. Divide this length by the number of loops then multiply by two. Your final answer is equal to the wavelength of the wave.
5, The frequency of the wave is the same as the frequency of the power supply.
Use the equation: wavespeed = frequency x wavelength
58
Ripple tank viewed from the top- shallow water
(The black lines represent peaks of waves) Water waves travel more slowly in shallow water. The wavelength of the waves also decreases.
59
What happens to the frequency when waves travel from one medium to another?
The frequency stays the same.
60
The wavelength in medium A is longer than in medium B when...
the speed in medium A is longer than in medium B when the speed in medium A is greater than the speed in medium B (true for all types of waves- sound and light).
61
What is a lens?
It is a piece of equipment that forms an image by refracting light.
62
Convex lenses
- In a convex lens, parallel rays of light are brought to a focus
- This point is called the principal focus
- sometimes referred to as the converging lens
63
What is the focal length and how does it alter?
- It is the distance from the lens to the principal focus.
- This depends on how curved the lens is
- The more curved the lens, the shorter the focal length
64
Concave lenses
- In a concave lens, parallel rays of light are made to diverge (spread out) from a point
- This lens is sometimes referred to as a diverging lens
- The principal focus is now the point from which the rays appear to diverge from.
65
representing convex lenses
arrow (head outwards)/ oval shape
66
representing concave lenses
arrow (head inwards)/ vase shape
67
Real image
- It is an image that is formed when the light rays from an object converge and meet each other and can be projected onto a screen
- A real image is one that is produced by the convergence of light towards a focus
- real images are always inverted
- Real images can be projected onto pieces of paper or screens. eg: an image formed on a cinema screen
- Real images are where two solid lines cross in ray diagrams.
68
Virtual image
- It is an image that is formed when light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen
- A virtual image is formed by the divergence of light away from a point
- Virtual images are always upright
- Virtual images cannot be projected onto a piece of paper or a screen eg:a person's reflection in a mirror.
- Virtual images are where two dashed lines, or one dashed and one solid line crosses in ray diagrams.
69
Lenses can be used to form
images of objects placed in front of them
70
Convex ray diagrams
If an object is placed further form the lens than the focal length f, then a real image will be formed, and the converging lens diagram will be drawn in the following way:
- Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line.
- Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus, f.
-The image is the line drawn from the axis to the point where the above two rays meet.
- When describing an image: consider if it is -
. real or virtual
. magnified (larger) or diminished (smaller)
. upright or inverted
real, magnified, inverted
71
real
The light rays meet each other after refraction
72
Magnified
The image is larger than the object
73
Inverted
The image is formed on the opposite side of the principal axis
74
When will a convex lens produce a real image?
When the object is placed at a distance greater than the focal length from the lens.
75
When will a convex lens produce a virtual image?
If the object is placed closer to the lens (converging ray diagram).
76
converging lens ray diagram - virtual image
1, start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line.
2, Draw a dashed line continuing this ray upwards
3, Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens, it will travel directly through the principal focus, f.
4, Also, draw a dashed line continuing this ray upwards
5, The image is the line drawn from the axis to the point where the two dashed lines meet.
virtual, magnified, upright
77
virtual
The light rays appear to meet when produced backwards
78
Magnified
The image is larger than the object
79
Upright
The image is formed on the same side of the principal axis
80
Concave (diverging) lenses can also be used to
form images, although the images are virtual in this case
81
Object placed further from the lens- concave lens ray diagram
-Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line
-Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly upwards away from the axis
-Draw a dashed line continuing this ray downwards to the focal point, f
-The image is the line drawn from the axis to the point where the above two rays meet
In this case, the image is:
Virtual: the light rays appear to meet when produced backwards
Diminished: the image is smaller than the object
Upright: the image is formed on the same side of the principal axis
82
Comparing convex and concave lenses
- The image produced by a convex lens can be either real or virtual
- This means the image can be inverted (real) or upright (virtual)
- The image produced by a concave lens is always virtual
- This means the image will always be upright
83
magnification =
image height/object height
84
What does the magnification depend on?
- the distance of an object from a lens
- the power of the lens
(the units for height are unimportant provided the units for image and object are the same)
85
Which colour has the longest wavelength?
Red (and the lowest frequency and energy)
86
Which colour has the shortest wavelength?
Violet (and the highest frequency and energy)
87
wavelength and frequency are
inversely proportional
88
An increase in wavelength is
a decrease in frequency (towards the red end of the spectrum)
89
A decrease in wavelength is
an increase in frequency (towards the violet end)
90
Specular reflection
- Reflection from a smooth surface in a single direction
- When light reflects off a smooth surface, such as a mirror, specular reflection occurs
- This is what gives a mirror its shiny appearance
- This is why a reflection can be seen clearly in a mirror
- In this case, the angle of reflection r is equal to the angle of incidence
91
Diffuse reflection
- reflection from a rough surface causes scattering
- When light reflects off a rough surface, which applies to the majority of surfaces, diffuse reflection occurs
- This is what gives objects a dull or matt appearance
- This is why a reflection cannot be seen clearly from a table surface, for example
- Even though a table’s surface may look smooth from afar, it is actually made up of many tiny ridges which the light rays are scattered off
- When light scatters, it leaves the surface in all directions
92
Colour filters
- White light is a mixture of all the colours of the spectrum
- Each colour has a different wavelength (and frequency), making up a very narrow part of the electromagnetic spectrum
- White light may be separated into all its colours by passing it through a prism
- This is done by refraction
- Violet light is refracted the most, whilst red light is refracted the least
- This splits up the colours to form a spectrum
- This process is similar to how a rainbow is created
93
Colour filters
-Colour filters work by absorbing certain wavelengths and transmitting other wavelengths
-These certain wavelengths correspond to certain colours
-When white light passes through a coloured filter, some colours are absorbed whilst others are able to pass straight through
-For example, when white light passes through a red filter:
Red light is transmitted
All the other colours are absorbed
-The colour that is transmitted is the same colour as the filter
94
The colour of an opaque object
-The colour of an opaque object is determined by which wavelengths of light are more strongly reflected
-Wavelengths that are not reflected are absorbed
Hence, this is why different objects appear to be different colours
-For example, white light upon a green surface will only have green light reflected and the others absorbed
-This light is reflected into our eyes to see the surface in that colour
95
When will an object appear white?
If all wavelengths are reflected equally
96
When will an object appear black?
If all wavelengths are absorbed
97
When will an object appear transparent?
If all the light is transmitted and only a small amount is reflected or absorbed.
98
What is the colour of an opaque object determined by?
Which wavelengths of light are most strongly reflected.
99
When light is incident on an opaque objects, it can only be
reflected or absorbed
100
eg: why does a box appear red?
- It absorbs all wavelengths of light except red. The red light is reflected into our eyes.
101
What are filters made of?
Transparent/translucent materials (lets light through). It only allows a small range of wavelengths to pass through.
102
red + green
yellow
103
red + blue
magenta
104
blue + green
cyan
105
All objects, whatever their temperature, emit and absorb
infra red radiation
106
An object hotter than its surroundings will
emit more radiation per second than it absorbs, to cool down.
107
What afects the emission and absorption of infrared radiation?
- temp gradient
- surface area
- material
- colour of surface
- texture
108
thermal equilbirum
When the rate of emission is the same as the rate of absorption of radiation, the temperature of the object does not change.
