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What 2 things do all electromagnetic waves have in common?
They are all transverse waves that transfer energy from a source to an absorber
All EM waves travel at the speed of light through air or a vacuum (space)
What’s the continuous spectrum of EM waves?
Waves have a range of frequencies they are ordered based on their frequency and wavelength
What happens to the frequency as you go up the continuous spectrum and why?
it increases due to having more energy
What happens to the wavelength as you go up the continuous spectrum?
wavelength decreases (gets shorter)
What is the order of the continuous spectrum?
Radio waves
Microwaves
Infrared
Visible light
Ultra violet
X-rays
Gamma rays
what do Radio waves do and how are they made?
Transfer energy
made by oscillating charges
What happen when charges oscillate?
They produce oscillating electric and magnetic fields (electromagnetic waves)
frequency of waves will be equal to the frequency of the alternating current
What’s the object where electrons oscillate to create radio waves?
A transmitter
What happens when radio waves reach a receiver?
They are absorbed
Energy is transferred to the electrons in the material
Causes electrons to oscillate
What are radio waves used for?
Mainly communication eg, FM (frequency modulation) radio, Tv, Bluetooth
Why are radio waves used for communication?
They have the longest wave length
Long wave lengths diffract (bend) around curved surfaces of the Earth, they can diffract over hills, into tunnels
Makes it possible for radio waves to be received even if receiver isn’t in a line of sight of the transmitter
Why can radio waves be received over long distances from transmitter?
They are reflected off of the ionosphere
What is the ionosphere?
An electrically charged layer in the Earth’s upper atmosphere
What’s FM transmissions?
frequency modulation
Have short wavelengths
Must be in direct sight of transmitter, signal doesn’t bend or travel through buildings
What are microwaves used for?
satellites
Microwave ovens
How are microwaves used in satellites?
microwaves can pass easily through the Earth’s watery atmosphere
Signal from transmitter is transmitted into space
Satellite receiver dish picks it up, whilst orbiting thousands of km above Earth, it transmits signal back to Earth in a different direction
Received by a satellite dish on the ground, there’s a time delay between transmitter and receiver due to the long distance
How do microwave ovens use microwaves?
microwaves are absorbed by water molecules in food
water molecules transfer energy to the rest of the molecules in the food by heating, this quickly cooks the food
What is Infrared radiation used for?
increase temperature
Monitor temperature
Eg. infrared camera, electric heaters, foods can be cooked
What gives off infrared radiation?
hot objects
The hotter the object, the more IR radiation is given out
How are infrared cameras used?
used to detect and monitor IR radiation
Turns it into an electrical signal, that’s displayed on a screen as a picture, hotter the object, the brighter it appears
Cooking food using IR radiation
absorbing IR causes objects to get hotter
IR radiation in electric heaters
contain long piece of wire, heats up as current flows through
Wire emits lots of IR radiation (and visible light, glows)
Emitted IR radiation is absorbed by objects and air in the room
Energy is transferred by IR waves to thermal energy stores of the objects, causing temperature to increase
What is visible light?
Light we can see
It’s made up of a range of colours
What’s visible light used for?
photography
Illumination
What’s the visible light spectrum?
A range of wavelengths that we perceive as different colours
Each colour has its own narrow range of wavelengths and frequencies
Colours can mix together to make other colours (can’t mix primary colours)
Order of the visible light spectrum
RED
ORANGE
YELLOW
GREEN
BLUE
INDIGO
VIOLET
What do colours of objects depend on?
Which ever wavelength of light are most strongly reflected
What’s fluorescence?
a property of certain chemicals
UV radiation is absorbed, visible light is emitted (giving you brightness)
Can be used to identify forged bank notes
What can UV radiation be used for?
security pens
Suntans
How do security pens work?
under UV light the ink will glow (fluorescent)
Invisible without UV light
Can help police identify property if stolen
What’s UV light produced by?
The sun
How is UV light dangerous?
tanning salons use UV lamps to give artificial suntan
They have hazardous properties (used to kill bacteria)
What are x-rays and gamma rays used for?
Medicine
How can x-rays be used
too look/identify broken bones
Tests for cancer (along with hammer rays)
Why are x-rays used to look/identify broken bones?
they can easily pass through flesh
Can’t pass through denser material (bones, or metal)
What gives you a x-ray?
The amount of radiation absorbed
how are gamma and x-rays used to kill cancer cells?
High doses kill all living cells, they are directed towards cancer cells, to avoid killing too many healthy cells
what are the jobs of radiographers
to use x-rays and gamma rays that treat people with cancer
What are radiographers?
people who work with x-rays and radiotherapy
What do radiographers use to protect them against rays?
wear lead aprons
Stand behind a lead screen
Leave the room
How can EM radiation be harmful to people?
High frequency waves (UV, X-ray, gamma) transfer lots of energy, causing damage to tissues
How is UV radiation dangerous?
can damage surface cells (sunburn)
Cause skin to age prematurely
Blindness or increase risk of skin cancer
How are x-rays and gamma rays dangerous?
they are types of ionising radiation
Can cause gene mutation (cancer)
Can lead to secondary cancer
How much likely are you to suffer damage to skin cells if you were to have a CT scan?
4 times more likely
Why are infrared cameras able to show parts of the hand at different temperatures?
Different temperatures emit different intensities of infrared, which are represented as different shades/colours on the camera
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