P 12 electromagnetic Waves Flashcards
(10 cards)
Properties of em waves
Transverse waves that transfer energy from source of waves to an absorber
All electromagnetic waves share following properties:
-all are transverse waves
-can all travel through a vacuum
-all travel at same speed in vacuum
The em spectrum
-electromagnetic spectrum is arranged in a specific order based on wavelengths and frequencies
Lower energy:
-long wavelength
-low fequency
-radio waves, microwaves, infrared
Higher energy:
-short wavelengths
-high frquency
-ultraviolet, x-rays, gamma rays
-the higher the frequency, the higher the energy of radiation
Radiation with higher energy is:
-highly ionising
-harmful to cells and tissues causing cancer
Radiation with lower energy:
-useful for communication
-less harmful to humans
Visible light
-defined as the range of wavelengths which are visible to humans
-visible light is only part of the spectrum detectable to human eye-only takes up 0.0025% of whole spectrum
-in natural world, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light
-the different colours of waves correspond to different wavelnegths:
Red has longest wavelength (lowest frequency and energy)
Violet had shortest wavelength (highest frequency and energy)
Tranfer of energy by em waves
-electromagnetic waves carry energy and so can transfer energy from one point to another point
-em radiation id sn energy transfer pathway
-em waves with a shorter wavelength carry a higher energy so more dangerous
Energy transfer by microwaves:
-water molecules absorb certain wavelengths of microwave radiation
-therefore microwave transfer energy by radiation to thermal store of food
Energy transfer by infrared:
-all hot objects emit infrared radiation
-the emitted waves can then be absorbed by other objects, warming them up
-therefore energy transferred by radiation to thermal store of object and surroundings
Energy transfer from sun:
-visible light waves allow living creatures to see
-infrared waves heat up earth
-ultraviolet waves cause suntans and sunburn
Em waves and atoms
-atoms interact with electromagnetic waves in of two wags-absorbed and emitted
-when em wave hits an atom, it can be absorbed by one kf the electrons giving it energy
Causes it to move up a higher energy level
-if an electron moves down to a lower energy level it will emit EM wave in process
-energies associated with electron transitions tend to br in visible and ultraviolet range
-higher energies can only be achieved when EM waves interact with nucleus
Radio waves
-an oscillator supplies carrier waves to the transmitter in the form of an alternating current
-the audio signal is supplied to the transmitter where it is used to modulate the carrier waves
-the modulated carrier waves from the transmitter are supplied to transmitter aerial. the varying ac current supplied to aerial causes it to emit radio waves that carry audio signal
-when radio waves are absorbed by a receiver aerial, they induce an ac current in receiver aerial, whic causes oscillations in receiver. The frequency of oscillations is the same as the frequency of radio waves
Radio communications
Carrier waves are the waves used to carry any type of signal
-they depend on how much information is in signal and the distance the signal has to travel
Radio wavelengths:
The shorter the wavelength of the waves:
-more information it can carry
-the shorter their range due to increased absorption by atmosphere
-the less spread out
-microwaves are used for satellite, phone and tv links because microwaves can travel between satellites in space and ground. Also, they spread out less than radio waves do, so the signal dose’t weaken as much
-radio waves are used for TV broadcasting fromTV masts as they can carry more information than longer radio waves
Optical fibre communications
-used to transmit signals carried by light or infrared radiation. Light rays can’t escape from fibre. When reach surface they are reflect back into fibre
-optical fibres carry much more information as light has a much shorter wavelength than radio waves, and so can carry more pulses of waves
-are more secure because the signals stay in fibre
Applications of em waves
Radio-communication (radio and tv)
Microwaves:
Heating food
Communication (wifi,mobile phones,satellites)
Infrarred:
-remote controls
-fibre optic communication
-thermal imaging
-night vision
-heating or cooking
-motion sensor
-cameras
Visible light:
-taking photographs
Ultraviolet:
-security markung
-fluorescent bulbs
-getting suntan
X-rays:
-X-ray imaging
Gamma rays:
-sterilising medical instruments
-treating cancer
Suitability of different em waves
Radio waves:
Use-for long-range communciations
Reason: because they can be reflected from earth atmosphere
Microwaves:
Use: satellite communciations
Reason: can penetrate through’s earth atmosphere
Infrared:
Use:optical fibre communication
Reason: can undergo total internal reflection
Visible light:
Use: taking photo’s or videos
Reason: cameras are set up to detect visible light
Ultraviolet:
Use: detecting security ink
Reason: because they have fluoresces with ultraviolet lighting
X-rays:
Use: to photograph bones
Reason: x-rays can penetrate soft tissues but not bond
Gamma rays:
Use: sterilise medical instruments
Reason: because gamma kills bacteria
Dangers:
High intensity microwaves can cause heating of internal organs as water molecules absorb microwaves strongly
Gamma -rays and high intensity uv can harm and cause cancer as they are highly ionising due to have a lot of energy
