EM Spectrum [REVISE]! Flashcards
electromagnetic spectrum is arranged in a specific order based on the ______________________
wavelengths or frequencies
longest wavelength (lowest frequency) to shortest wavelength (highest frequency)
goes
RMIVUXG
red monkey in van under xray, gamma!
Radio waves
Microwaves
Infrared
Visible (red, orange, yellow, green, blue, indigo, violet)
Ultraviolet
X-rays
Gamma rays
The higher the frequency, the higher the energy of the radiation
^ FREQ,
^ ENERGY OF RADIATION
Radiation with higher energy is:
Highly ionising
Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
Radiation with lower energy is:
Useful for communications
Less harmful to humans
RADIO & GAMMA,
which wl is shorter?
Radios are big (long wavelength)
Gamma rays are emitted from atoms which are very small (short wavelength)
Properties of Electromagnetic Waves
Define them
Transverse waves that transfer energy from the source of the waves to an absorber
All electromagnetic waves share the following properties:
all transverse
They can all travel through a vacuum
They all travel at the same speed in a vacuum
continuous spectrum
speed of electromagnetic waves in a vacuum is
3.0 × 10^8 m/s
approximately the same speed as electromagnetic waves in air
Uses of Electromagnetic Waves
- RADIO
communication (radio & TV)
- Used for long-range communications
- Reason: because they can be reflected from the earth’s atmosphere
- microwave
DANGER PREVENTED
Microwave ovens, on the other hand, emit very large amounts of energy, however, that energy is prevented from escaping the oven by the metal walls and metal grid in the glass door
heating food
communication (WiFi, mobile phones, satellites); microwaves emit very small amounts of energy which are not known to cause any harm
- Use: satellite communications
- Reason: bc microwaves can penetrate earth’s atmosphere
- infra-red
📍 remote controls
📍 fibre optic communication (MOST) ;;
⭐ USE - OPTICAL FIBRE COMMUNICATION
⭐ REASON ;;; bc they can UNDERGO TOTAL INTERNAL REFLECTION
📍 thermal imaging (medicine & industry, research)
📍 night vision
📍 heating or cooking things
📍 motion sensors (for security alarms)
📍 electrical heaters
📍 infrared cameras
- visible light
seeing & taking photographs/videos
⭐ USE: taking photos & videos
⭐ REASON: Cameras are SET UP TO DETECT VISIBLE LIGHT
fibre optic communications
/// only part of the electromagnetic spectrum that the human eye can see; human eye can detect wavelengths from 750 nanometres (red light) up to 380 nanometres (violet light)
- ultraviolet
security marking (fluorescence)
⭐ USE: for DETECTING SECURITY IK
⭐ REASON: bc it FLUORESCES w/ ULTRAVIOLET LIGHTING
fluorescent bulbs (energy efficient lamps)
getting a suntan [your body’s way of protecting itself against the ultraviolet]
- X-Rays
X-Ray images (medicine, airport security & industry)
⭐ USE: to PHOTOGRAPH BONES
⭐ REASON: bc x-rays can penetrate soft tissues but NOT bone; able to pass through most body tissues but are absorbed by the denser parts of the body, such as bones
When exposed to x-rays, the bones absorb the x-rays, leaving a shadow which can be seen using a special x-ray detector or photographic film
- Gamma rays
⭐ USE: sterilising medical instruments
⭐ REASON: bc GAMMA KILLS BACTERIA
treating cancer;; very dangerous and can be used to kill cells and living tissue; property can be utilised in both cancer detection and treatment
If these gamma rays are carefully aimed at cancerous tissue, they can be very effective at destroying the cancerous cells
DANGERS:
- MICROWAVES
Danger: high intensity microwaves can cause heating of internal organs
REASON: water molecules absorb microwaves strongly
- GAMMA, X-RAYS, UV
Danger: Gamma x-rays & high intensity ultraviolet can HARM CELLS & CAUSE CANCER
Reason: they are HIGHLY IONISING due to having a LOT of energy
Dangers - general. Main risks associated with EM waves
- Radio
No known danger
- Microwave
Possible heat damage to internal organs;
Certain frequencies of microwaves are absorbed by water molecules
Since humans contain a lot of water, there is a risk of internal heating from microwaves
Infrared
skin burns
visible light
bright light can cause eye damage
Ultraviolet
eye damage [Good quality sunglasses will absorb ultraviolet, preventing it from entering the eyes]
sunburn
skin cancer [Sunscreen absorbs ultraviolet light, preventing it from damaging the skin]
X-rays
able to penetrate the body and cause internal damage
Kills cells
mutations
cancer
[radiation badges are worn by medical professionals such as radiographers to measure the amount of radiation exposure in their body; leave room]
Gamma rays
able to penetrate the body and cause internal damage
kills cells
mutations
cancer
SUBSTANCES ->
exposed to ultraviolet ->
absorb & re-emit as visible light.
When certain substances are exposed to ultraviolet, they absorb it and re-emit it as visible light (making them glow)
This process is known as fluorescence
Fluorescence can be used to secretly mark things using special ink – in fact, most bank notes have invisible fluorescent markings on them
Fluorescent light bulbs also use this principle to emit visible light
frequency increase =
energy increase
Beyond the visible part of the spectrum, the energy becomes large enough to __________
ionise atoms
danger associated with EM waves
increases along with the frequency
The shorter the wavelength, the more ionising the radiation ;;
ionising meaning it can kill cells or cause them to malfunction, resulting in premature ageing, and diseases such as skin cancer
The shorter the wavelength, the more ionising the radiation
but intensity of wave, type of radiation and the size of the dose also plays important role
Communications with Satellites
what’s used
Geostationary and polar orbiting (low orbit) satellites
both used for communicating information
polar = vertical
Geostationary Satellites
Geostationary satellites orbit above the Earth’s equator
The orbit of the satellite is 24 hours
At a height of 36 000 km above the Earth’s surface, much higher than polar satellites
Used for radio and telecommunication broadcasting around the world due to its high orbit
Polar satellites
Polar, or low orbit, satellites orbit around the Earth’s north and south poles
These orbit much lower than geostationary satellites, at around 200 km above sea level
Used for monitoring the weather, military applications, and taking images of the Earth’s surface
There is a much shorter time delay for signals compared to geostationary orbit signals
The signals and images are much clearer due to the lower orbit
However, there is limited use in any one orbit because more than one satellite is required for continuous operation
Systems of Communications
Many important systems of communications rely on LONG wave electromagnetic radiation, including:
Mobile phones, wireless internet & satellite television (using microwaves)
Bluetooth, terrestrial television signals & local radio stations (using radio waves)
Optical fibres (using visible or infrared waves)
Radio Waves; SHORT
e.g.
can be used to transmit signals over short distances
Terrestrial (local) television signals, radio station transmissions [[ transmitted at a longer wavelength than local TV signals ]] & Bluetooth all work using radio waves
In hilly areas, it may be possible to receive radio signals but not receive terrestrial television signals
because?
radio signals are more prone to diffraction around the hills
Radio signals…
tend to have wavelengths of around a kilometer, so the radio signals are more likely to have wavelengths similar to the size of the hill
leads to diffraction, so radio signals can reach locations not in the line of sight of the transmitter, whereas TV signals are not diffracted
bluetooth uses…
uses radio waves instead of wires or cables to transmit information between electronic devices, over short distances, such as phones and speakers
bluetooth tends to have
shorter wavelengths than radio or television signals
enables high rates of data transmission, but can only be used over a short distance (for example, within a household)
means they can pass through walls but the signal is significantly weakened on doing so
microwaves - LARGE.
used to transmit signals over large distances
Microwaves are used to send signals to and from satellites
microwaves - e.g.s
As with radio waves, microwave signals will be clearer if there are no obstacles in the way which may cause diffraction of the beam
Mobile phones, wireless internet, satellite (global) television and monitoring Earth systems (for example, weather forecasting) all utilise microwave communication
microwaves from a dish
must be s____ compared to… & m____ bc…
When microwaves are transmitted from a dish, the wavelength must be small compared to the dish diameter to reduce diffraction
Also, the dish must be made of metal because metal reflects microwaves well
Mobile phones and wireless internet use microwaves
why?
microwaves are not refracted, reflected or absorbed by the atmosphere or ionosphere
therefore
means satellites can relay signals around the Earth enabling 24-hour-a-day communication all around the world
can penetrate most walls and only require a short aerial for transmission and reception
Optical Fibres
used for?
used for cable television and high-speed broadband
because?
because glass is transparent to visible light and some infrared
Also, visible light and short-wavelength infrared can carry high rates of data due to their high frequency
two types of signals:
Analogue
Digital
analogue -
e.g.
📍 Analogue signals vary continuously - they can take any value; consists of varying frequency or amplitude
e.gs of analogue technology: telephone transmission and some broadcasting
digital -
📍 can only take one of two (discrete) states
; is generated and processed in two states:
1 or 0 (high or low states respectively)
usually referred to as:
along y-axis
1s and 0s
Highs and lows, or
Ons and offs
Transmission of Sound (sound waves can be transmitted as a digital or analogue signal)
Signals for speech or music are made up of…
varying frequencies
for info to be clear
signal needs to be transmitted with as little interference as possible
signal goes is converted both before transmission and after being received
Before transmission: AD
signal is converted from analogue to digital
After being received: OPPOSITE.
the signal is converted from digital to analogue
Benefits of Digital Signalling
key advantages of transmission of data in digital form compared to analogue are:
- signal can be regenerated so there is minimal noise
2.
Due to accurate signal regeneration, the range of digital signals is larger than the range of analogue signals
DIGITAL COVERS LARGER DISTANCES
3.
Digital signals enable an increased rate of transmission of data compared to analogue
4.
Extra data can be added so that the signal can be checked for errors
