Waves Flashcards
(84 cards)
1
Q
What is a longitudinal wave?
A
Vibrations move parallel to (along) the direction the energy travels
2
Q
Examples of longitudinal waves:
A
- Sound
- Some seismic waves
3
Q
What is a transverse wave?
A
Vibrations move perpendicular (in a different direction) to the direction the energy travels
4
Q
Examples of transverse waves:
A
- Water waves
- EM waves
- Some seismic waves
5
Q
Amplitude
A
The maximum distance a particle moves away from its resting position when a wave passes
6
Q
The higher the amplitude, the ………… energy the wave has
A
The more energy the wave has
7
Q
Wavelength
A
The distance between a point on one wave & the same point on the next wave, usually peak to peak
8
Q
Period (of a wave):
A
The time taken for one complete wave to pass a fixed point (measured in seconds)
9
Q
Wavefront
A
A line joining points on a wave at the same point in their wave cycle at a given time
10
Q
What do waves transfer?
A
Waves transfer energy and information from one place to another without transferring matter.
11
Q
Equation for wavespeed:
A
Wavespeed (m/s) = Frequency (Hz) x Wavelength (m)
12
Q
Equation for frequency:
A
Frequency (Hz) = Number of waves (waves) / Time (s)
13
Q
How do you measure the velocity of ripples on water surfaces?
A
- Make some ripples
- Count the number of waves that pass a point in a fixed time
- Frequency = number of waves / time
- Take a photo & measure the wavelength
- Velocity = Frequency x wavelength
14
Q
The Doppler Effect
A
The apparent change in observed wavelength and frequency of a wave emitted by a moving source relative to an observer
15
Q
What happens to the frequency and wavelength when a wave source moves toward an observer?
A
- Frequency increases (higher pitch for sound, blue shift for light).
- Wavelength decreases (waves are compressed).
16
Q
What happens to the frequency and wavelength when a wave source moves away from an observer?
A
- Frequency decreases (lower pitch for sound, red shift for light).
- Wavelength increases (waves are stretched out)
17
Q
What does a stationary wave source emit?
A
Emits at a constant wavelength & frequency
18
Q
Explain the Doppler Effect and give an example:
A
- If a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength due to the doppler effect
- because the wavefronts either get bunched up or spaced apart
- e.g. when the siren of an ambulance is high pitched as it approaches you, and low pitched as it goes away
19
Q
Reflection
A
When a wave bounces off a surface instead of passing through it or being absorbed
20
Q
The law of reflection
A
Angle of incidence = Angle of reflection
21
Q
In reflection, frequency, wavelength & speed are all ……
A
Unchanged
22
Q
Refraction
A
The change in direction when a wave goes from one medium to another
23
Q
What happens to the wave from a less to more dense medium?
A
→Wave slows down
→Bends towards normal
24
Q
What happens to the wave from a more to less dense medium?
A
→Waves speed up
→Bends away from the normal
25
Electromagnetic waves all:
1. Travel at the speed of light
2. Can travel through a vacuum
3. Are transverse
26
What is the order of the electromagnetic spectrum from low to high frequency?
- Radio waves
- Micro-waves
- Infrared
- Visible light
- Ultra-Violet
- X-Rays
- Gamma Rays
27
What is the order of the electromagnetic spectrum from short to long wavelength?
- Gamma
- X-Rays
- UV
- Visible Light
- IR
- Micro-waves
28
We can see a mix of all colours as ….. light
White
29
The absence of light is seen as ………
Black
30
Uses: Radio waves
- Broadcasting, communications & satellite transmissions
- They have long wavelengths & are reflected by the ionosphere
31
Dangers from excessive exposure: Radio waves
None
32
Uses: Microwaves
- Cooking, communications & satellite transmissions
- Shorter wavelength than radio means they can penetrate the ionosphere & food
33
Dangers from excessive exposure: Microwaves
Internal heating of body tissue
34
Uses: Infrared
- Cooking, infrared imaging, heating, short range communications & television remote controls
- Their wavelengths makes them able to penetrate short distances & deposit enough energy to heat objects
35
Dangers from excessive exposure: Infrared
Skin burns
36
Uses: Visible light
- Sight, photography, illumination & optical fibres
- We see wavelengths of visible light
- Visible light can travel through glass wires (optical fibres) by total internal reflection
37
Dangers from excessive exposure: Visible light
Damage to the retina at the back of the eye
38
Uses: Ultraviolet
- Security marking & fluorescent lamps
- When some substances absorb UV, they will emit visible light (called fluorescents)
39
Dangers from excessive exposure: Ultraviolet
- Damage to surface cells & eyes, leading to skin cancer & blindness
- Sun cream & sunglasses help prevent excessive exposure
40
Uses: X-Rays
- Observing the internal structure of objects, including airport security scanners & medical X-rays
- Because of their short wavelength, X-rays easily penetrate soft materials but are absorbed by more dense materials
41
Dangers from excessive exposure: X-rays
- X-Rays are ionising, they can cause cell mutation leading to cancer
- Protective (lead) shielding helps prevent excessive exposure
42
Uses: Gamma rays
- Sterilising food & medical equipment
- Gamma’s high energy can kill cells including pathogens
43
Dangers from excessive exposure: Gamma rays
- Gamma-Rays are ionising, they can cause cell mutation leading to cancer
- Protective (lead) shielding helps prevent excessive exposure
44
What type of wave is light?
Transverse
45
What are two key properties of light waves?
Light waves can be reflected and refracted.
46
What happens when light is reflected?
Light bounces off a surface at the same angle it arrived (Law of Reflection: Angle of incidence = Angle of reflection).
47
What happens when light is refracted?
Light changes direction when passing from one medium to another due to a change in speed.
48
How do we represent waves in diagrams?
Waves are shown as ruler-straight lines with arrows indicating direction.
49
What is an incident ray?
A ray of light traveling toward an interface or object.
50
What is a reflected ray?
A ray of light that has been reflected from a surface.
51
What is the normal in a ray diagram?
An imaginary line at right angles to the surface where the light ray hits
52
What is the angle of incidence?
The angle between the incoming ray and the normal.
53
What is the angle of reflection?
The angle between the reflected ray and the normal.
54
Practical (3.17/3.19)
The best way to determine refractive index is:
1. Shine a ray of light through the material, at an angle
2. Measure the angle of incidence, from the normal, with a protractor
3. Measure the angle of refraction, from the normal, with a protractor
4. Plot a graph of sin i against sin r
5. Gradient = refractive index
55
PRACTICAL: investigate the refraction of light, using semi-circular blocks
1. Place a glass block on paper and draw around it
2. Use a ray box so that single beam of light is incident on the curved side of the glass block.
3. Draw two crosses on the incident beam & two crosses on the emergent beam.
4. Remove the glass block and using a ruler, join up the two crosses on the incident and emergent rays.
5. Join up these beams by drawing the path of light through the block.
6. Using a protractor, measure the angles of incidence, refraction & emergence from the normal.
7. Repeat with different angles of incidence.
56
PRACTICAL: investigate the refraction of light, using triangular prisms
1. Place a glass block on paper & draw around it
2. Use a ray box so that single beam of light is incident on the glass block.
3. Draw two crosses on the incident beam & two crosses on the emergent beam.
4. Remove the glass block and using a ruler, join up the two crosses on the incident and emergent rays.
5. Join up these beams by drawing the path of light through the block.
6. Using a protractor, measure the angles of incidence, refraction, & emergence from the normal.
7. Repeat with different angles of incidence.
57
PRACTICAL: investigate the refraction of light, using rectangular blocks (3.17)
1. Place a rectangular glass block on paper and draw its outline.
2. Shine a ray of light at an angle into one side of the block.
3. Mark the incident ray, refracted ray, and emerging ray.
4. Draw a normal line at the point of entry and measure the angles of incidence and refraction using a protractor.
5. Observe that the light bends towards the normal when entering (denser medium) & bends away when exiting (less dense medium). The emerging ray is parallel to the incident ray but displaced.
58
What is refractive index?
(Optical density)
A measure of how much a material slows down light waves, & therefore, how much they refract
59
Equation for refractive index:
refractive index (n) = angle of incidence (sin i) / angle of refraction (sin r)
60
What happens to light in a right-angled prism?
Light is totally internally reflected, making the image appear at 90° to & below the object.
61
Why is total internal reflection better than mirrors?
In total internal reflection, no light is lost, making it more efficient than mirrors.
62
What are optical fibres made of?
plastic or glass with a cladding that has a lower refractive index than the core
63
How does light travel through optical fibres?
by total internal reflection
64
What is the advantage of optical fibres?
can bend to reach difficult places
65
What happens when a ray goes from dense to less dense?
The ray refracts away from the normal
66
What is the critical angle (c)?
The critical angle is when the ray refracts at 90° to the normal & the angle of incidence equals the critical angle
67
What happens if the angle of incidence is greater than the critical angle?
If the angle of incidence is greater than the critical angle, the ray undergoes total internal reflection
68
Equation for critical angle:
Critical angle (sin c) = 1 / refractive index (n)
69
What type of wave is sound?
Longitudinal wave
70
Can sound waves be reflected and refracted?
Yes
71
What is the frequency range for human hearing?
20 Hz to 20,000 Hz
72
PAPER 2 What are frequencies below 20 Hz called?
Frequencies below 20 Hz are called infrasound
73
PAPER 2 Ultrasound
Frequencies greater than 20,000 Hz
74
PRACTICAL: investigate the speed of sound in air (microphones)
1.Use Speed=distance/time
2.Measure the distance between two microphones using tape measure
3.Distance must be more than 1m
4.Measure the time it takes the sound to travel from microphone A to microphone B using an electronic timer
5.Repeat & take an average
75
PAPER 2 To calculate distance between an emitter & a detector:
Distance = time x wave velocity
76
PAPER 2 To calculate distance from an echo:
2 x distance = time x wave velocity
Distance = (time x wave velocity) / 2
-Because the wave has travelled the distance twice in the measured time
77
PAPER 2 PRACTICAL: investigate the speed of sound in air (clap)
1.Use Speed = distance / time
2.Measure the distance between two students using a trundle wheel
3.Distance must be more than 100m
4.Measure the time between seeing the clap & hearing the clap using a stopwatch
78
PAPER 2 How can microphones and oscilloscopes be used to display a sound wave?
- Microphones detect sound waves and convert them into electrical signals.
- Oscilloscopes display these signals as a trace on a screen.
79
PAPER 2 What does the oscilloscope display show?
The oscilloscope shows the sound wave with:
- X-axis = time
- Y-axis = amplitude
80
PAPER 2 PRACTICAL: investigate the frequency of a sound wave using an oscilloscope
1.Connect oscilloscope to microphone
2.Adjust the oscilloscope to get a steady trace
3.Adjust time base to give a minimum of one complete cycle on the screen
4.Measure the number of squares for one complete cycle
5.Multiply the number of squares by the time base to find time period, T
Use frequency (f)= 1/(time period (T)
81
PAPER 2 How does the pitch of a sound relate to the frequency of vibration of the source?
Higher frequency = Higher pitch
82
PAPER 2 How does the loudness of a sound relate to the amplitude of vibration of the source?
Higher amplitude = Louder sounds
83
PAPER 2 How is sound produced?
when matter vibrates & these vibrations are passed onto other particles
84
PAPER 2 What is the direction of vibration in sound waves?
Vibrations are parallel to the direction the wave travels
