light (half chapter) Flashcards
speed of light,refraction,white light & prism, addition & subtraction of colours, absorbing and reflecting colours
Who was Ole Romer?
He was a Danish astronomer who observed the moons of Jupiter and studided how they travelled around the planet.
What did the Ancient Greece believe?
They believed that light travelled at infinite speed.
What did Romer discover after studying teh eclipses more thoroughly?
He discovered that they appeared to occur earlier when Earth was nearer Juipter in its orbit than it was further away.
What did the other scientists found?
That Juipter was between Earth and one of its moons, the moon could not be seen from the Earth and was said to be eclipsed by Jupiter. The large 4 moons move roung jupiter quickly & scientists found it hard to time.
What didn’t Romer believe and what did he believe?
He didn’t believe that the moons speeded up at different times of the year. He believed that the difference was due to llight having finite speed and took longer to reach Earth
How did Romer find out the time?
After taking measurements and making calculations, it showed that it took 11 minutes from Sun to Eath.
Who was James Bradley?
He was an English astronomer who studied the stars position at different times. He calculated the speed of light which took 8 minutes and 11 seconds to travel.
Who was Armand Fizeau?
He was a French physicist who made an instrument which measured the speed of light from a candle 9km away. He calculated that light travels at a speed of 314 262 944m per sec.
what is the speed of light in vacuum and what is average mean time take?
Speed of light in is 299 992 460m/s in vacuum slightly slower in air and even slower in water and glass. rounded to 300 000 000 m/s. average time is 8 minutes and 17 seconds.
What is refraction and angle of refraction?
The bending of light ray is known as refraction. The angle that the refracted ray makes with the normal is called angle of refraction.
Why does the light ray bend when going from one medium to another?
It bends due to the change of speed the light. Air: 300 million m/s, Glass: 200 million m/s. When the ray slows down from one medium to another the ray bends towards the normal, but if its the opposite in speed, the ray bends away.
what is a triangular prism?
a glass or plastic block with a triangular cross section.
what is spectrum?
when a ray is shone through a prism at certain angles of incidence and path is stopped by white screen, it disperse into a range of colours.
what is dispersion?
the splitting of white light. it occurs due to the different colours of light travel at very slightly different speeds and refracted at slightly diiferent angles
Write newtons investigation with prisms.
he put a prism which he brought at a fair and placed it in a dark room and shone sunlight onto it from a window. the light entered and dispersed to form a spectrum onto the white screen. then he got a second prism and set it behind the first one but opposite way round and when the spectrum passed through the second prism they formed a beam of white light.
absorbing and reflecting colours
when all colours are reflected the object will appear white and if its absorbed the the object will appear black.
Filtering colours
sheets of coloured galss or plastics are used to filter the colours. the colour is produced by dyes which are put into the filter when it is being made. each filters absorbs all the colurs in white lught except red meaning when white light shines on red filter all colours are absorbed except red. all colours have been subtracted except red
addition and subtraction
red, green and blue are primary colours of light and when when 3 are shown onto a white screen they overlap producing 3 secondary colours and white light.
colours mixing of light
blue+ green= cyan
red+blue= magenta
red+green=yellow
all= white
addition and subtraction definition
addition: adding/combining of three colours of light.
additive colour mixing: mixing of light
subtracting: when ray is passed through blue filter, all clours are absorbed except blue all colours have been subtracted
where does the ray refracts?
light refracts at the boundary between air and glass or air and water.
