Topic 6 - Waves Flashcards
1
Q
What do
waves do?
A
they transfer energy from one place to another without transferring any matter
2
Q
Define
amplitude.
A
the maximum displacement of a point on the wave from its undisturbed position
3
Q
Define
wavelength.
A
the distance between the same point on two adjacent waves
4
Q
Define
frequency.
A
the number of complete waves passing a certain point per second
this is measured in Hz, 1Hz is 1 wave per second
5
Q
What is the
crest
of a wave?
A
the maximum positive displacement of a point on the wave from its undisturbed position
6
Q
What is the
trough
of a wave?
A
the maximum negative displacement of a point on the wave from its undisturbed position
7
Q
What is the
period
of a wave?
A
the time it takes for a full cycle of the wave
8
Q
What equation allows you to calculate the
period
of a wave?
A
period = 1 / frequency
T = 1/f
T: s
f: Hz
9
Q
What are the
two different types of waves?
A
transverse and longitudinal
10
Q
What is the relationship between oscillations and direction in a
transverse wave?
A
the oscillations are perpendicular to the direction of energy transfer
11
Q
What is the relationship between oscillations and direction in a
longitudinal wave?
A
the oscillations are parallel to the direction of energy transfer
12
Q
What are some examples of
transverse waves?
(3)
A
- all electromagnetic waves (e.g. light)
- ripples and waves in water
- a wave on a string
(most waves are transverse)
13
Q
What are some examples of
longitudinal waves?
(2)
A
- sound waves in air, ultrasound
- shock waves (e.g. some seismic waves)
14
Q
What is
wave speed?
A
the speed at which energy is being transferred
(the speed the wave is moving at)
15
Q
What wave equation links
frequency, speed and wavelength?
A
wave speed = frequency x wavelength
v = fλ
v: m/s
f: Hz
λ: m
16
Q
Describe how you would use an
oscilloscope to measure the speed of sound.
(6 steps)
A
- Attach a signal generator to a speaker (so that you can generate sounds with a specific frequency).
- Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
- Start with both microphones next to the speaker.
- Slowly move on away until the two waves are aligned on the display (but have moved exactly one wavelength apart.
- Measure the distance between the microphones to find one wavelength.
- You can then use the wave formula to find the speed of the sound wabes passing through the air.
(the frequency is whatever you set the signal generator to)
around 1kHz is sensible
17
Q
What is the
speed of sound in air?
A
around 330m/s
18
Q
Describe how you would
measure the speed of water ripples usig a lamp.
(5 steps)
A
- Attach a signal generator to the dipper of a ripple tank in order to create water waves at a set frequency.
- Use a lamp to see wave crests on a screen below the tank. Make sure the size of the waves’ shadows are the same size as the waves.
- The distance between each shadow line is equal to one wavelength.
- Measure the distance between shadow lines that are 10 wavelengths apar, then divide this by 10 to find the average wavelength.
- Use the wave equation to calculate the speed of the waves.
If you’re struggling to measure the distance, you could take a photo of the shadows and ruler, and find the wavelength from the photo instead.
19
Q
Describe how you would calculate the
speed of waves on string.
(7 steps)
A
- On one end of a bench, attach a signal generator to a vibration transducer.
- On the other end, attach a pulley.
- Attach a piece of string to the vibration transducer, over the pulley and attach some masses on the end.
- Turn on the signal generator and vibration transducer (the string will start to vibrate).
- Adjust the frequency of the signal generator until there’s a clear wave on the string.
- You need to measure the wavelength of these waves.
- You can find the speed of the wave using the wave equation.
(the frequency of the wave is whatever the signal generator is set to)
The best way to accurately measure the wavelength is to measure the lengths of four or five half-wavelengths in one go, then divide to get the mean half-wavelength. (You can then double this mean to get a full wavelength.)
20
Q
What are the 3 things that can happen when
waves arrive at a boundary between two different materials?
A
- The waves are absorbed by the material the wave is trying to cross into (transferring energy to the material’s energy stores)
- The waves are transmitted (they carry on travelling through the new material)
- The waves are reflected
21
Q
What is the
rule for all reflected waves?
(to do with angles)
A
angle of incidence = angle of reflection
i = r
22
Q
What is the
point of incidence?
A
the point where the wave hits the boundary
23
Q
What is the
normal?
A
the imaginary line that’s perpendicular to the surface at the point of incidence
this is usually shown as a dotted line
24
Q
What is the
angle of incidence?
A
the angle between the incoming wave and the normal
25
# What is the
angle of reflection?
the angle between the **reflected wave** and the normal
26
# What is
specular reflection?
| and give an example.
when a wave is reflected in a **single direction** by a **smooth surface**
| e.g. when **light** is reflected by a **mirror**
## Footnote
(resulting in a nice, **clear reflection**)
27
# What is
diffuse reflection?
| and give an example
when a wave is reflected by a **rough surface** and the reflected rays are **scattered** in **lots of different directions**
| e.g. a **piece of paper**
28
# What causes an object to appear
matte vs shiny?
When **light** is reflected by a rough surface, the surface appears **matte** as you **don't** get a **clear reflection**
| (the opposite occurs with smooth and so shiny objects)
29
# What are
electromagnetic waves?
**transverse** waves that come from vibrations of electrical and magnetic fields
| this means that they can travel through a vacuum
30
# What are the
seven basic types of EM waves?
| (in order of ascending frequency)
**R**ich - **R**adio Waves
**M**en - **M**icro Waves
**In** - **In**fra Red
**V**egas - **V**isible Light
**U**se - **U**ltra Violet
**X**pensive - **X**-rays
**Ga**dgets - **Ga**mma Rays
31
# What is the range of wavelength of
radio waves?
10^4 m - 1m
32
# What is the range of wavelength of
micro waves?
1m - 10^-2 m
33
# What is the range of wavelength of
infra red?
10^-2 m - 10^-5 m
34
# What is the range of wavelength of
visible light?
10^-5 m - 10^-7 m
35
# What is the range of wavelength of
ultra violet?
10^-7 m - 10^-8 m
36
# What is the range of wavelength of
x-rays?
10^-8 m - 10^-10 m
37
# What is the range of wavelength of
gamma rays?
10^-10 m - 10^-15 m
38
# Why is there such a
large **range of frequencies** of EM waves?
because EM waves are **generated** by a **variety** of changes in **atoms** and their **nuclei**
## Footnote
this also explains why atoms can **absorb** a range of frequencies - each one causes a **different change**
39
# When does
refraction occur?
when a wave crosses a **boundary** between materials at an **angle** and it **changes direction**
40
# What affects how much a wave is
refracted?
how much the wave **speeds up** or **slows down**
| (which usually depends on the **density** of the two materials)
## Footnote
usually the **higher** the density of the material, the **slower** a wave travels through it
41
# What happens when a wave crosses a boundary an
slows down?
it will bend **towards** the **normal**
| (and vice versa - a wave that speeds up will bend away from the normal)
42
# What happens if the wave is travelling
across a boundary between materials along the normal?
it will **change speed**, but it's **NOT refracted**
43
# Describe an experiment that investigates
refraction through different materials.
| (6 steps)
1. Place a transparent rectangular box on a piece of **paper** and **trace around it**.
2. Use a **ray box** or a **laser** to shine a ray of light at the **middle** of one side of the block.
3. **Trace** the **incident ray** and **mark** where the light ray **emerges** on the other side of the block.
4. Remove the block and, with a **straight line**, **join up** the **incident ray** and the emerging point to show the path of the **refracted ray** through the block.
5. Draw the **normal** at the **point** where the light ray entered the block. Use a **protractor** to measure the **angle of incidence** and the **angle of refraction**
6. **Repeat** this experiment using rectangular blocks made from different materials, keeping the **incident angle** the **same** throughout.
44
# How can you produce
radio waves?
1. **EM waves** are made up of **oscillating electric and magnetic fields**.
2. **Alternating currents** are made up of **oscillating** charges. As the charges oscillate, they produce **oscillating electric and magnetic fields** (EM waves).
3. **Radio waves** are produced using an alternating current in an electrical circuit.
45
# How are
radio waves transferred?
| (4 steps)
1. The **transmitter** oscillates electrons to **create** the radio waves.
2. When the transmitted radio waves reach a **receiver**, the radio waves are **absorbed**.
3. The **energy** carried by the waves is **transferred** to the **electrons** in the material of the receiver.
4. This energy causes the electrons to **oscillate** and (if the receiver is part of a complete electrical circuit) it generates an **alternating current**.
| this current has the same frequency as the radio wave that generated it
46
# What is the main use of
radio waves?
communication
47
# What are the wavelengths of
radio waves?
long-wave radio?
short-wave radio?
radio: >10cm
long-wave: 1-10km
short-wave: 10-100m
48
# How far can
long-wave radio be transmitted?
| and why?
they can be transmitted halfway around the world because long wavelengths **diffract** (**bend**) around the curved surface of the Earth
49
# What is the
ionsphere?
an electrically charged layer in the Earth's upper atmosphere
50
# How far can
short-wave radio signals be transmitted?
| and why?
they can be transmitted large distances because they are **reflected** from the **ionsphere**
51
# Why must you be in
**direct sight of the transmitter** to get reception for **TV and FM radio**?
because the transmissions have very short wavelengths that cannot bend or travel far **through** buildings
52
# What types of wave does
communication to and from satellites use?
| and why?
microwaves
| they can **pass easily** through the Earth's **water atmosphere**
53
# How do
microwaves work?
| (3 steps)
1. The **microwave oven** releases microwaves.
2. These penetrate a few centimetres into the food before being **absorbed** and **transferring** the energy they are carrying to the **water molecules** in the food, causing the water to **heat up**.
3. The water molecules the **transfer** this energy to the rest of the molecules in the food **by heating** - which **quickly cooks** the food.
54
# What is
infrared radiation?
radiation that is **given out** by all **hot objects**
| the **hotter** the object, the **more** IR radiation it gives out
55
# How do
electric heaters work?
| (3 steps)
1. Current flows through a **long piece of wire** that **heats up**.
2. This wire **emits** a lot of **infrared radiation**.
3. The emitted IR radiation is **absorbed** by objects and the air in the room - energy is transferred **by the IR waves** to the **thermal energy stores** of the objects, causing their **temperature** to **increase**.
56
# What are
optical fibres?
| and how do they work?
they are thin **glass or plastic fibres** that can **carry data** over long distances as pulses of **visible light**
## Footnote
the light rays are **bounced back and forth** by **reflection** until they reach the end of the fibre
57
# What is
fluorescence?
a property of certain chemicals where **UV** radiation is **absorbed** and then **visible light** is **emitted**
58
# How do
fluorescent lights work?
| and why are these good?
1. The lights generate **UV radiation**.
2. This is absorbed and **re-emitted as visible light** by a layer of **phosphor** (on the inside of the bulb)
| they're very **energy-efficient**
59
# How is an
x-ray image created?
It's the amountof radiation that's **not absorbed** that gives you an X-ray image.
X-rays pass **easily through flesh** but no so easily through **denser material** like **bones** or **metal**.
60
# What are
two uses of x-rays?
- seeing if someone has any **broken bones**
- treatment for **cancer**
61
# What are the effects of each type of radiation when it
enters living tissue?
| (categorised by frequency)
- **Low frequency** waves (e.g. **radio waves**) mostly **pass through soft tissue** without being absorbed
- **High frequency** waves (**UV**, **x-rays**, **gamma rays**) transfer **lots** of energy and so can cause **lots of damage**
62
# What are the effects of
UV radiation entering living tissue?
| (general + 4 consequences)
It damages surface cells.
This can lead to:
- sunburn
- skin aging prematurely
- blindness
- increased risk of skin cancer
63
# What are the effects of
x-rays or gamma rays enterring living tissue?
| (general + 3 consequences)
It can knock electrons off atoms.
This can lead to:
- gene mutation
- cell destruction
- cancer
64
# What is
**radiation dose**?
| and what is this measured?
a measure of the **risk** of harm from the body being exposed to radiation
| this is measure in **sieverts** (Sv)
65
# What is the
axis of a lens?
a line passing through the **middle** of the lens
66
# What does a
convex lens do?
It **bulges outwards**, causing rays of **light** parallel to the axis to be **brought together** (**converge**) at the **principal focus**.
67
# What does a
concave lense do?
It **caves inwards**, causing rays of **light** parallel to the axis to **spread out** (**diverge**).
68
# What is the
principal focus?
| (in both concave and convex lenses)
conex lens - where rays hitting the lens all **meet**
concave lens - where rays hitting the lens **appear** to all **come from**
69
# Define
focal length.
the **distance** from the **centre of the lens** to the **principal focus**
70
# What are the three key things to mention when
describing an image?
1. **How big it is** compared to the object.
2. Whether it's **upright or inverted** relative to the object.
3. Whether it's **real or virtual**.
71
# How is a
convex lens represented in ray diagrams?
↑
|
↓
72
# How would you
draw a ray diagram for an image through a convex lens?
| (6 steps)
1. Pick a point on the **top** of the object.
2. Draw a ray going from the object to the lens **parallel** to the axis of the lens.
3. This ray is **refracted** through the **principal focus** (F) on the **other side** of the lens.
4. Draw another ray from the **top** of the object going right through the **middle** of the lens. (This ray doesn't bend.)
5. Mark where the rays **meet**. That's the **top of the image**.
6. Repeat the process for a point on the bottom of the object.
73
# How does
distance from the lens affect the image for a convex lens?
| (an object at 2F, between F and 2F and nearer than F)
- an object **at 2F** will produce a **real**, **inverted** image the **same size** as the object, and at **2F** (on the other side of the lens)
- an object **between F and 2F** will make a **real**, **inverted** image **bigger** than the object, and **beyond 2F**
- an object **nearer than F** wil make a **virtual** image the **right way up**, **bigger** than the object, on the **same side** of the lens
74
# How is a
concave lens represented in ray diagrams?
a vertical line with an arrow head pointing inwards on each side
75
# How would you
draw a ray diagram for an image through a concave lens?
| (6 steps)
1. Pick a point on the **top** of the object.
2. Draw a ray going from the object to the lens **parallel** to the axis of the lens.
3. This is **refracted** so that it appears to have come from the **principal focus**. Draw a **ray** from the principal focus. Make it **dotted** before it reaches the lens.
4. Draw another ray from the top of the object going right through the **middle** of the lens. (This lens doesn't bend.)
5. Mark where the refracted rays **meet**. That's the top of the image.
6. Repeat the process for a point on the bottom of the object.
76
# What are the rules surrounding the
image produced by a concave lens?
A **concave** lens always produces a **virtual image**. The image is the **right way up**, **smaller** than the objet and on the **same side of the lens as the object**.
| The further an object is from the lens, the smaller the image produced.
77
# What is the
formula for magnification?
magnification = image height / object height
| I = AM
78
# What are the three
primary colours of light?
red
green
blue
79
# What are
opaque objects?
objects that **do not transmit light**
| they **absorb** some wavelengths and **reflect** others
## Footnote
**transparent** and **translucent** objects **transmit light**
80
# What wavelengths of light are reflected for an object that is
not a primary colour?
| (2 options)
- the **wavelengths** of light corresponding to that **colour** are reflected
- the wavelengths of the **primary** colours that can **mix together** to make that colour are reflected
81
# What wavelengths of light do
white objects reflect/absorb?
they **reflect all** of the wavelengths of visible light **equally**
82
# What wavelengths of light do
black objects reflect/absorb?
they **absorb all** of the wavelengths of visible light
| your eyes see black as the **lack of** any visible light
83
# What is a
transparent or translucent object's colour related to?
the wavelengths of light **transmitted** and **reflected** by it
84
# How does
temperature affect how much IR radiation an object emits and absorbs?
| (3 steps)
- an object that's **hotter** than its surroundings **emits more IR radiation** than it **absorbs** as it **cools down**
- an object that's **cooler** than its surroundings **absorbs** more IR radiation than it **emits** as it **warms up**
- objects at a **constant temperature** emit IR radiation at the **same rate** that they are **absorbing it**
85
# How do
colour and surface finish affect how well at absorbing and emitting radiation an object is?
**black** + **matte** - **better** at absorbing and emitting radiation
**white** + **shiny** - **worse** at absorbing and emitting radiation
86
# Describe a practical that
investigates IR radiation emission with a Leslie cube.
| (6 steps)
1. Place an **empty Leslie cube** on a **heat-proof** mat.
2. **Boil** water in a kettle and **fill** the **Leslie cube** with boiling water.
3. Wait for a while for the cube to **warm up**, then hold a **thermometer** against each of the four vertical faces of the cube. (These should all be at the **same temprature**.)
4. Hold an **infrared detector** a **set distance** away from one of the cube's vertical faces, and record the **amount of IR radiation** it detects.
5. **Repeat** this measurement for **each** of the cube's **vertical faces**.
6. Do this experiment **more than once**, to make sure your results are **repeatable**.
87
# Define
perfect black body.
an object that **absorbs all** of the radiation that hits it
| **no** radiation is **reflected** or **transmitted**
## Footnote
these are also the **best possible emitters** of radiation
88
# What is the relationship between
temperature and intensity of wavelengths emitted by an object?
as the **temperature** of the object **increases**, the **intensity** of **every emitted wavelength** increases
| the intensity **increaes more rapidly** for **shorter wavelengths**
89
# What happens to
radiation from the sun that reaches Earth's atmosphere?
- some radiation is reflected by the atmosphere, clouds and the Earth's surface
- some radiation is absorbed by the atmosphere, clouds and the Earth's surface
- some radiation is also emitted from each surface
90
# What type of wave are
sound waves?
longitudinal waves
| sound waves are caused by vibrating objects
91
# Describe how you
hear sound?
| (when your ear drum vibrates)
1. Sound waves reach yourm **ear drum** and cause it to **vibrate**.
2. These **vibrations** are passed on to **tiny bones** in your ear called ossicles, through semicircular canals and to the cochlea.
3. The **cochlea** turns these vibrations into **electrical signals** which get sent to your brain and allow you to **sense** the sound
92
# What is the range of frequencies a
human ear can hear?
20Hz - 20kHz
93
# When are
sound waves reflected?
when they hit a **hard flat surface**
94
# When are
sound waves refracted?
when they enter **different media**
## Footnote
as they enter **denser material**, they speed up
95
# What is
ultrasound?
sound with frequencies higher than 20 000Hz
96
# What is
partial reflection?
when a wave passes from one medium into another and **some** of the wave is **reflected** off the boundary and some is transmitted
97
# What are
three uses of ultrasound?
- medical imaging
- industrial imaging
- echo sounding
98
# How can ultrasound be used in
medical imaging?
| (2 steps)
1. Ultrasound waves can pass through the body, but whenever they reach a boundary between **two different media** (e.g. fluid in the womb and the skin of the foetus) some of the wave is **reflected back** and **detected**.
2. A computer can process the exact **timing and distribution** of these **echoes** to produce **video image** of the foetus.
99
# How can ultrasound be used in
industrial imaging?
| (2 steps)
1. Ultrasound waves entering a material will usually be **reflected** byt the **far side** of the material.
2. If there is a flaw such as a **crack** inside the object, the wave will be **reflected sooner**.
| this helps to find flaws in objects
100
# What is
echo sounding?
the use of ultrasound to find out the **depth of the water** a boat or submarine is in
101
# What are the
two different types of seismic waves?
| (that you need to know)
P waves and S waves
102
# How are
seismic waves created?
when there's and **earthquake** somewhere, it produces **seismic waves** which travel through the Earth
103
# How are
seismic waves detected?
using seismometers
104
# What are the key characteristics of
P-waves?
| (4)
## Footnote
- type of wave?
- types of substances they can travel through?
- relative speed?
- can they travel through the Earth's core?
- they are **longitudinal**
- they travel through **solids** and **liquids**
- they travel **faster** than **S-waves**
- they can travel through the **Earth's core**
105
# What are the key characteristics of
S-waves?
| (4)
## Footnote
- type of wave?
- types of substances they can travel through?
- relative speed?
- can they travel through the Earth's core?
- they are **transverse**
- they can't travel through **liquids** or **gases**
- they're **slower** than **P-waves**
- they cannot travel through the **Earth's core**
