Electromagnetic Spectrum Flashcards
(61 cards)
1
Q
what are electromagnetic waves
A
electromagnetic waves are electric and magnetic disturbances that transfer energy (not matter) from a source to an absorber
2
Q
what speed does all electromagnetic waves travel at?
A
3 x 10^8 m/s
3
Q
what is the equation of wave speed, frequency and wavelength
A
wave speed (m/s) = Frequency (Hz) x Wavelength (m)
v = f x λ
4
Q
what order does the electromagnetic spectrum go in from the longest wavelength to the shortest
A
Radio, Microwave, Infrared, Visible light, Ultra- Violet, X-rays, Gamma rays
5
Q
Are EM waves transverse or longitudinal
A
Transverse
6
Q
Does energy increase or decrease from radio to gamma waves
A
Energy increases
7
Q
Does the frequency increase towards Gamma or radio
A
Increase frequency towards gamma
8
Q
Is wavelength larger at microwave or gamma
A
- Wavelength larger towards radio
- small wavelength towards Gamma
9
Q
There is a large range of frequencies because EM waves are generated by …….
A
- a variety of changes in atoms and their nuclei e.g. change in the nucleus of an atom creates gamma rays
10
Q
White light contains what colours?
A
contains all the colours of the spectrum
11
Q
what colour has the shortest and longest wavelength
A
Shortest: Violet
Longest: Red
12
Q
What are EM waves made up of?
A
oscillating electric and magnetic fields
13
Q
How are EM waves produced?
A
- EM waves made up of oscillating electric and magnetic fields
- Alternating currents (AC) are made up of oscillating charges.
- As the charges oscillate, they produce oscillating electric and magnetic fields, i.e. electromagnetic waves.
- frequency of the waves = frequency of the AC
14
Q
how are radio waves produced
A
- using alternating current in a electrical circuit
- Transmitter produces a oscillating current to create a radio wave
- frequency of alternating current = frequency of radio wave
- receiver absorbs the energy/ radio waves
- energy carried by waves is transferred to the electrons in the material of the receiver
- energy causes the electrons to oscillate , and if receiver is part of a complete electrical circuit a alternating current is generated
- current has same frequency to the radio wave
15
Q
Radio waves are EM radiation with wavelengths longer than about …… cm
A
10
16
Q
How are long- wave radios used for communication? why is it useful
A
- long wavelengths can diffract(bend) around the curved surfaces on the Earth
- can diffract around hills, into tunnels
- makes it possible for radio waves to be received even if the receiver isn’t in the line of sight of the transmitter
17
Q
What is the wavelength of long-wave radios
A
1 - 10km
18
Q
What is the wavelength of short-wave radio signals
A
10-100m
19
Q
How are short- wave radio signals used for communication?
A
- can be received* at long distances from the transmitter
- they are reflected from the ionosphere - electrically charged layer in the Earths upper atmosphere
20
Q
Uses of radio waves
A
- radio player
- Bluetooth
- Broadcasting TV (Satellite communication)
21
Q
Does Bluetooth use long or short wave radio signals and how
A
Short-wave
- to send data over short distances between wireless devices*
22
Q
what can medium-wave signal do
A
can also reflect form the ionosphere, depending on atmospheric conditions + time of day
23
Q
Does TV and FM radio use long or short wave radio signals and why?
A
-TV and FM transmissions have very short wavelengths
-need to transfer a lot of information
- to get reception must in direct sight of transmitter
- signal doesn’t bend or travel far through buildings
24
Q
Uses of Infrared:
A
- infrared cameras
- Remote controls
- Electrical heaters
- Ovens
25
How and what are infrared imaging used for?
- to **detect infrared radiation**
- ** monitor temperature**
- camera **detects IR temperature** and turns it into an **electrical signal**
- **displayed** on the **screen** as a **picture**
- **hotter** the object is, **brighter** it appears
26
Absorbing Infrared radiation causes objects to get ……
hotter
27
How to Electrical heaters work ?
- contain **long piece of wire** that **heats up** when a **current flows** through
-wire then **emits** lots of **infrared radiation**(and a little **visible light**- glows )
- **emitted IR absorbed** by objects and air in surroundings
- energy is transferred by IR waves to **thermal energy stores** of objects --> **temp inc.**
28
Energy is transferred by **the ……. Waves** to the …… of the objects, causing their …… to …….
Infrared
Thermal energy stores
Temperature
Increase
29
Uses for Microwaves:
- microwave ovens
- mobile phones
- satellite communication
30
Why are microwaves the best for communicating satellite signals
- **pass easily** through Earth’s **watery atmosphere**
- spread out less than radio waves, **signal doesn’t weaken** as much
31
How is satellite TV signals transmitted?
- signal from transmitter, transmitted into **space**
- signal picked up by **satellite receiver dish ORBITING** thousand of km above **Earth**
- **satellite transmits** the **signal** back to **Earth** in a **different direction**
- it's **received** by a **satellite dish** on the **ground**.
- There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel.
32
How do Microwave ovens work?
- **microwaves** **absorbed** by **water molecules** in food
- microwaves **penetrate** up to a **few centimetres** into the **food** before being **absorbed** and **transferring the energy** they carry to the **water molecules** in the food, causing the water to **heat up.**
- **water molecules** then **transfer energy** to the **rest of the molecules** in the food by **heating** - which guickly cooks the food.
33
Uses of Visible light:
- Optical Fibres
- Cameras
- Endoscopes
- Torches
34
What are optical fibres
- *thin glass** or **plastic fibres** that can **carry data** over **long distances** as pulses of **visible light**
35
How to optical fibres work/
- **reflection** of **visible light**
- light rays **bounce back and forth** until end of fibre
- light is not easily **absorbed** or **scattered** as it travels along a fibre
36
Radio waves of different frequencies are used for different purposes because the wavelength (and so the frequency) of waves affects:
- how far they can travel
- how much they spread
- how much information they
can carry.
37
Uses of Ultraviolet
- security pens
- fluorescent lights
- bank note identification
- UV tanning
38
What is Fluorescence
- property of certain chemicals, wher **UV** radiation is **absorbed** and **visible light ** is **emitted**
39
how do fluorescent lights work
- fluorescent lights generate **UV radiation**, which is absorbed and **re-emitted as visible light** by a layer of **phosphor** on the inside of the bulb
40
what are the advantgaes of Fluorescent lights
- **energy efficient**
- so good for **long periods**
41
when are security pens used
- mark property with name (laptops)
- help **identify** property of stolen
42
how do security pens work
- under **UV light** ink will **glow** (fluoresce), but **invisible** otherwise**
43
Waves can transfer …. And ……
Energy, information
44
What are Carrier waves and examples
Waves that carry **information**. Do this by **varying their amplitude**
- radio waves
- microwaves
- infrared radiation
- visible light
45
Why do shorter wavelengths carry more information and what are the disadvantages
- shorter wavelength = **higher frequency** so more waves arrive quicker
- **more information transferred**
- Disadvantage: **range is less**, due to **increase absorption** by the **atmosphere**
46
Uses of gamma radiation:
- killing harmful bacteria in food or surgical equipment
- radiotherapy
- medical tracer
47
Uses of X-rays
- X-ray imaging / Radiotherapy
48
why does ionisation occur in X-rays and Gamma rays
- when x-rays or gamma rays pass through a substance
- **knock electron out** of their **atoms** in substance
- if ionisation happens to **living cells** it can **damage cells**
- **Gene mutations, cell destruction, cancer**.
49
how do X-rays work
- pass **easily through flesh**
- not so easily through **denser materials** - bones, metal
- **amount of radiation absorbed** = image
- **brighter** areas are where **fewer X-rays** get through --> **negative image**
50
how is gamma radiation used in a medical tracer
- **gamma-emitting source** is injected into patient
- **progress** is followed around the body
51
why is gamma suited to be a medical tracer
can pass out the body to be detected, wont stay in too long - has short half life
52
What can X-rays be blocked by
- bones
- teeth
- metal inside body
53
How can we X-rays soft tissue organs?
- filling organs with a **contrast medium**
- **absorbs X-rays**
- enables **internal surfaces** in the organ to be **seen** on radiograph
54
Radiation does is a measurement of what
The **damage** done to their **body** by **ionising radiation**
55
What 3 things does the radiation does depend on:
- radiation types
- time exposed
- energy per second absorbed (surface area, concentration )
- different parts of body (chest vs head)
56
Dangers of UV radiation
- damage surface cells
- can lead to **sunburn**
- **skin to age prematurely**
- **blindness**
- **increase risk** of **skin cancer**
57
what are precautions against X-ray and gamma
- lead aprons
- lead screen
- leave room
- safety film badge
58
is radio waves harmful, why
no
- **Low frquency** wave - dont transfer much energy
- mostly **pass through soft tissue** without being absorbed
59
why do UV, Xray, gamma have harmful effect
- **High frequency**
- transfer **lots of energy
- **lot of damage**
60
what is radiation dose measured in
Sieverts
61
what is radiation dose
a measure of the **risk** of harm of the body being exposed to radiation
