11.6 EM spectrum Flashcards
- different wavelengths
- how aerial works
- everything to do with optic cables
- some more pints for tar
Skim
What are EM waves
Transverse waves of electric and magnetic fields oscillating at 90° to each other and to the direction of wave travel
How are they defined?
Radio micro infra red Visible and ultra violet by their wavelengths
As their is an overlap between wavelengths of x ray and gamma, these are defined differently : x rays are Fast emitting electrons, gamma rays come from unstable nuclei
Radio wavelength
> 10^6 to 10^-1
So more than a million to 0.1 m
Microwaves
0.1m to 0.001m
10^-1 to 10^-3m
Infrared
0.001 m to 0.7 micrometers
10^-3 to 7x10^-7
Visible
0.7 micrometers to 0.4 micrometers
Ultraviolet
0.4 micrometers to 100 Nano meters
4x10^-7 to 10^-8
X rays and gamma rays
100 to 1 manometers roughly x ray
Anything above 10^-13 is gamma
What about colours?
Just like infra red has higher wavelength, red has highest wavelength and ultraviolet or VIOLet colour has highest frequency .
How does white light get dispersed in a prism
Different speeds in, red faster so refract less, violet slower but reflects more , then split
How do aerials reduce interference and why you need to alligned
To reduce interference some groups will transmit vertically polarised or horizontally polarised waves , thus the type of waves increase reducing interference .
You alligned so it aligns with the polarised waves, else you sill get a component and that reduces
Fibre optic cables
What two things must happen that makes data good and why !!
- fibres are highly transparent to minimise absorption of light = loss of signal, have very low critical angle so always reflects
- core must be very narrow to prevent modal (multi path ) dispersion
- this is preventing light arriving at different times or merging , Lowe bandwidth
Critical angle?
Going to lower refractive index
Going beyond critical angle
If not tir then what will always happen?
Refraction + reflection
