em waves types Flashcards
What are all em waves
Transverse
where do all em waves travel the same speed in
a vacuum
what speed do they travel in it
3x10 to the power of 8
how do they transfer energy
from a source to an absorber
give an example
ir radiation emitted from hot object absorbed by surrounding air
what is the em wave spectrum ordered in
the increasing frequency and decreasing wavelength or increasing wavelength and decreasing frequency
what is the part of the spectrum humans can see
visible light
what is an alternating current made of
oscillating charges
what does the frequency of the ac current determine
the frequency of wave we produce
what device transmits and recieves the ac
transmitter and reciever
what can we transfer using radio waves
nearly all types of information
what are very short radio waves used for
fm radio or tv
why do you get faulty radio signal when in the car
hills and surrounding other objects interfere with the direct
transmission path of the wave
what uses medium radio waves used to send data
bluetooth
what do oscilloscopes display
wave frequency of an alternating current
what are 2 types of microwaves
ones absorbed by water molecules and ones not absorbed by water molecules
what and how are the non water microwaves used for
communication using satelites. they pass through atmosphere which has a lot of water
how are they used
recieved by satelite and transmitted back down to earth detected by satelite dish to get satelite tv
how are water microwaves spread through food
conduction and convection
what is ir radiation used for
ir cameras /cooking in oven and grills without penetrating surface of food/electric heaters
how are oven and grills using ir radiation
metal is heated with ir and emits ir radiation
how are live organisms detected by ir cameras
they are hotter then surroundings so emit more ir radiation and appear brighter on ir camera
what allows visible light to be used for communication
optical fibres that transmit data fast over long distances without absorbing and or scattering light(specular)
why are optical fibres used over copper wires
they can transmit much more data and there is less chance for it to be distorted in transmission
what uses uv light that is human generated
sun beds
what are x rays used for
viewing internal structure of the body
what do staff operating x rays wear
lead aprons
why are gamma rays used
to sterilise medical equipment and food and in medical tracers
why are they used over boiling water
as they kill microorganisms without melting equipment or altering food
what is the trade off
they can diagnose and treat disease but also ionise cells
what is convex
a lense that bulges ouwards
What is the focal point/principal focus
The point that rays of light converge
how does a lens form an image and how does it help us to see an image better
they help us to see an image as sharper or larger(magnifying glass/microscope)
it forms an image by refracting light
what are real images always
inverted
virtual image are made from
2 imaginary lines
what rays do concave lenses produce
virtual images
what are virtual images
always upright
concave lenses always produce
upright virtual images and the further they are from the lens the larger they are
do virtual images form projections on screens
no
what images can come from concave lenses vs convex lenses
concave - virtual
convex-virtual and real
roygbiv
red orange yellow green blue indigo violet
what has longest wavelength and highest
red has longest and violet has the shortest so the highest freq/energy
what is specular reflection
reflection from a smooth surface in a single direction(eg mirror
what is diffuse reflection
reflection from a rough surface that causes scattering(eg matte/why reflection cant be seen off a table)
what is white light
a mixture of all colours in the soectrum
the more freq/energy the more
the light is refracted
How do colour filters work
They absorb certain wavelengths(colours) and transmit others
The colour transmitted is
The colour of the filter
Colour of an opaque object depends on
The wavelengths of light that are reflected the strongest
wavelengths that are not reflected
are absorbed
white light on a green surface will have
green reflected into our eyes
object appears white
when all wavelengths re absorbed equally
appears transparent when all light is transmitted an only some is reflected or absorbed
all light is transmitted an only some is reflected or absorbed
body is in equilibrium when
it absorbs radiation at the same rate it emits radiation
object appears black when all wavelengths are absorbed
when all wavelengths are absorbed
Temperature can be regulated by
controlling how much incoming radiation is absorbed or emitted
rescue teams use light coloured shiny emergency blankets
as they emit less radiation than dark matt surfaces keeping patient warm as less ir is emitted
