p13 - electromagnetic waves Flashcards
define electromagnetic waves
- electric and magnetic disturbances
- travel as waves and transfer energy from a source to an absorber
how are electromagetic waves grouped?
from longest wavelength, smallest frequency to shortest wavelength and highest frequency
give order of electromagnetic waves
- radio waves (wavelengths upto 10^4 m)
- microwaves
- infrared radiation
- visible light
- ultra violet
- x rays
- gamma rays (wavelengths as short as 10 to the power of -15)
the higher the frequency of an electromagnetic wave…
the more energy it transfers
give equation for wavespeed
v = f x wavelength
wavespeed (electromagnetic: 3 x 10^8 m/s) = frequency (Hz) x wavelength (m)
define visible light
- each colour has a different wavelength which increases fron violet to red
- using different shades and colours within visible light is important in photography
define white light
mixture of all the colours in visible lights
define infrared radiation
- emitted by all objects
- hotter the object, the more radiation it emits
- used in remote controls for TVs and DVD players
- can be transmitted along optical fibres, used in special cameras to see in dark
define microwaves
- used in communications
- microwave transmitters produce wavelengths that can pass through atmosphere
- used to send signals to and from satellites for TV programmes
- used in microwave ovens for heating food
define radio waves
used to transmit radio and TV programmes
what radiation do mobile phones use?
- microwave radiation
- radio-waves at near microwave frequencies
give a hazard of microwave and radio wave radiation
- penetrate skin and absorbed by body tissue causing internal heating that is very damaging
give a hazard of infrared radiation
- absorbed by skin and too much causes burns
define carrier waves
waves used to transfer any signal
why are the radio and microwave spectrum divided into different bands
different bands used for differenct communications purposes
the shorter the wavelength of the waves…
- the more information they carry
- the shorter their range
- the less they spread out
why are microwaves used for satellite phone and TV signals?
they can travel between satellites in space and Earth
why are optical fibres carrying visible light of infrared radiation useful in communications?
- they carry much more information that radio and microwave transmissions
- more secure because waves stay in fibre
define an audio signal
- produced by a microphone when sound waves reach it
- used to modulate carrier waves
how are carrier waves used to transmit information?
1) M - audio signals modulate carrier waves
2) S - supplied by transmitter waves
3) I - radio waves induce AC current
4) S - reciever circuits separates audio signals from carrier circuits
5) S - audio signal supplied to loudspeaker
6) E - emits sound waves
define ultraviolet waves
- used for security marking and sunbeds
- cause sunburn and skin cancer
- may be harmful to human eyes
define x-rays
- used to make images of bones to check for fractures
- to detect cracks in metal objects
define gamma rays
- used to kill harmful bacteria in food to prevent food poisoning
- to sterilise surgical instruments
- may cause cancer but can also kill cancer cells
what happens when gamma and x-rays pass through substances?
- knock electrons out of atoms in substances
- leaves atoms with a positive charge
- process called ionisation
- kills or damages living cells
what are lead screens used for and why does this work?
- to shield people who work with x-rays and gamma rays
- this works because lead absorbs x-rays and gamma rays
define a ‘film badge’
for people who work with ionising radiation to monitor worker’s exposure to it
how can x-rays check for bone fractures and x-ray problems?
- pass through soft tissure but absorbed by bones, teeth (and metal objects)
define charge-couples devices
an electronic device creating an electronic signal from an optical image formed on the CCD’s array of pixels
how can soft organs be seen on x-ray image?
filled with a contrast medium tht absorbs x-rays
define radiation dose
measure of damage done by radiation
how can cancerous cells be destroyed?
by using high energy x-rays
