Electromagnetic Waves Flashcards
What’s the connection between light, microwaves and X-rays?
They are all different types of electromagnetic radiation that travel as waves and transfer energy from a source to an absorber.
Electromagnetic Spectrum
Radio waves
Microwaves
Infrared
Visible Light
Ultra violet
X-rays
Gamma rays
what has the longest wavelength?
radio waves
what has the shortest wavelength?
gamma rays
what has the lowest frequency?
radio waves
what has the highest frequency?
gamma rays
wave speed equation?
Wave speed = frequency X wavelength
So, in a vacuum all EM waves travel at approximately…………..
300 million metres per second!
What is the relationship between frequency and wavelength of EM waves?
As the frequency increases, the wavelength decreases
What is the relationship between frequency of EM waves and energy carried?
Higher frequency waves carry more energy.
Properties of electromagnetic waves
Transfer energy from a source to an absorber.
Can be reflected and/or refracted at boundaries.
Are absorbed as they travel through matter (how quickly depends on the substance and the wavelength of the EM wave)
uses of radio waves
Radio waves are used for communication such as television and radio. Radio waves are transmitted easily through air. They do not cause damage if absorbed by the human body, and they can be reflected to change their direction. These properties make them ideal for communications.
uses of microwaves
Microwaves are used for cooking food, communications and for satellite communications. Intense sources of microwaves can be dangerous through internal heating of body cells.
uses of infared
Infrared (IR) light is used by electrical heaters, cookers for cooking food, short-range communications like remote controls, optical fibres, security systems and thermal imaging cameras which detect people in the dark.
uses of visible light
Visible light is the light we can see, so is used in photography and illumination. It is also used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.
Why can’t we use radio waves to send and receive signals from satellites?
Microwaves can pass through the atmosphere, radio waves cannot.
What danger does IR radiation pose?
Burn, damage or kill skin cells as it heats them up.
What is white light?
A mixture of all the colours of light in the visible part of the EM spectrum.
Ultraviolet Comes from:
The sun (& UV light bulbs)
Ultraviolet Used for:
Killing bacteria in water
Detecting forged banknotes
Security markers
Sunbeds (but…..!)
Crosslinking polymers
Finding evidence in crime investigations
Photo-therapy for some medical conditions, including jaundice and psoriasis.
Ultraviolet Dangers:
Eyes: Cataract
Skin: Sunburn, premature aging (wrinkles!) and skin cancer.
X-Rays Made when:
electrons, or other particles moving at high speed, are stopped. Produced in X-ray tubes
X-Rays Used for:
Medical imaging
Security imaging
Detecting cracks in metal objects
Treating cancer
x rays Dangers:
X-rays are a form of ionising radiation.
The ionising properties of X-rays mean that they can damage the DNA in cells. The ionising effect of X-rays is more damaging to actively dividing cells in the body.
Low doses of X-rays may cause cancer.
High doses can kill cells.
Cancer treatment
Cancer is a disease in which cells divide in an uncontrolled way because of changes in their DNA. This can form tumours.
One method of treating cancer is to direct high energy X-rays or gamma rays at the tumours. This causes so much damage to the cancerous cells that they die. This treatment is called radiotherapy.
problems with radiotherapy
It is important that the gamma radiation hits the cancerous cells without hitting too many of the healthy cells.
To do this, more than one beam of radiation is used.
This means that less of the healthy cells are damaged by the radiation.
Gamma rays Produced:
Nucleus of atoms following alpha (α) or beta (ß) emission.
Gamma rays Uses:
Radiotherapy
Killing bacteria by irradiation
Reduce spoilage of food
Kill pathogens (Salmonella and clostridium)
Sterilise medical instruments
gamma rays dangers:
Exposure can damage cell DNA which
can cause cancer.
what happens to x rays inside the human body
x rays are absorbed by bone
x rays travel through skin
what happens to ultrasound inside the human body
it is partially reflected when it meets a boundary between two different media
travels at different speeds through different media
Put these in order of increasing frequency:
radio waves, microwaves, IR, visible light, UV, X-rays, gamma rays
Which type of EM wave is used for Bluetooth communication?
Radio waves
How does the colour and surface of an object affect the rate it emits IR radiation?
Dark, matt objects absorb and emit IR radiation at a faster rate than light coloured shiny objects.
Much of our communication is now carried by 4 types of EM wave:
Radio waves
Microwaves
Light
Infrared radiation
Which radio wavelength would you choose for a local radio station
Medium (1 - 100m)
They don’t need a very long range, and they don’t need to carry too much information so a medium wavelength is used.
Which radio wavelength would you choose for a national radio station
Long ( more than 100m)
These need to have a long range, so longer wavelengths are used
Which radio wavelength would you choose for a TV station
Short ( less than 1m)
TV signals carry images, so they carry more information than just the sound used in radio. Therefore they need a shorter wavelength.
why are microwaves used for satellite links
Microwaves are used for satellite links because they are capable of getting through the ionosphere
How are the radio signals transmitted?
Radio waves are transmitted from radio masts by applying alternating current.
These radio waves are detected by an aerial and their frequency causes an alternating potential difference to be induced in the receiver.
Radio wave signals are split into bands of different wavelength ranges.
How radio works
An oscillator supplies carrier waves (which carry the signal) to the transmitter in the form of an alternating current (changes direction all the time)
At the radio station, a microphone produces audio waves when sound waves reach it.
Audio waves are supplied to the transmitter.
The transmitter combines the audio waves and carrier waves = modulated radio waves.
The modulated radio waves are supplied to the transmitter aerial.
The aerial emits the modulated radio waves that carry the signal.
Radio waves are absorbed by the receiver aerial and induces AC (frequency is the same as the radio wave).
The audio waves are supplied to a loudspeaker which sends out sound waves.
Radio waves Vs. microwaves
Satellite TV signals are carried by microwaves. We can detect the signals on the ground because they can pass straight through a layer of ionised gas in our upper atmosphere.
This layer of gas, called the ionosphere, reflects longer wavelength, lower frequency radio waves back to earth.
how are texts sent?
Microwaves carry signals between your mobile phone and the nearest mobile phone mast.
The signal is sent using a carrier wave which is modulated (changing the frequency or amplitude) to include the information in your text message.
The message is then forwarded to the recipient through the phone network, then to their phone from their closest mobile phone mast.
Are mobile phones safe?
Mobile phones use similar waves to
microwave ovens. For this reason,
some scientists believe they can be
harmful - especially to children because
they have thinner skulls than adults.
Optical Fibres
Optical fibres use light and IR to transfer information.
These waves have a shorter wavelength than radio, so they can carry more information.
The signals are contained within thin optical fibres and cannot escape, so optical fibres are more efficient.
Advantages of optical fibres
They are very secure : the signal stays in the fibre so they cannot be intercepted
light and IR waves have a shorter wavelength and higher frequency than radio waves. More pulses are transmitted every second so more information can be sent.
investigating absorption with melting wax:
1) two ball bearings are each stuck to one side of a metal plate with solid pieces of candle wax. the other sides of these plates are then faced towards the fame
2) the sides of the plates that are facing towards the flame each have a different surface colour, one is matte black and one is silver.
3) the ball bearing on the matte black plate will fall first as the black surface absorbs more infrared radiation - transferring more energy to the thermal energy store of the wax. this means the wax on the black plate melts before the wax on the silver plate.
investing emission:
1) place an empty Leslie cube on a heat proof mat.
2) boil a kettle and fill the Leslie cube with boiling water.
3) wait for the cube to warm up, then hold a thermometer against each of the four vertical faces of the cube. you should find that all four faces are the same temperature
4) hold an infrared detector a set distance away from one of the cubes vertical faces, and record the amount of IR radiation it detects
5) repeat this measurement for each of the cubes vertical faces. make sure you position the detector at the same distance from the cube each time
6) you should find that you detect more infrared radiation from the black surface that the white one and more from the matt surfaces than the shiny ones
7) as always you should do the experiment more than once to make your results more repeatable
precautions when investigating emission practical
dont move the cube when its full of boiling water, you might biurn your hands
be careful when carring a kettle
