5.5 More about interference Flashcards
are double slits coherent sources
yes because they emit light waves of the same frequency with a constant phase difference provided we use a narrow slit of light or a laser
what makes them coherent
each crest or trough from the single slit passes throuhgone of the double slits at a fixed term after the first slit
why can’t light from two nearby bulbs form an interference pattern
the two light sources emit light waves at random
the points of cancellation and reinforcement would change at random so no interference pattern would be possible
what does the fringe pattern separation in light depend on
the colour of light used
what colour is the fringe separation greater than blue
red
this is because it has a longer wavelength than blue and fits into the formula
what do vapour lamps and discharge tubes produce
light with a dominant colour
e.g the sodium vapour lamp produces a yellow/orange glow which is due to the wavelength 590nm
other wavelength are emitted but this is the most intense
in effect it is a monochromatic light source because its spectrum is dominated by a certain colour
what is light from a filament lamp or the sun composed of
the colours of the spectrum and therefore covers a continues range of wavelength from 350nm to 650nm
when white light is directed at a colour filter why is the light a particular colour
it contains a much narrower range of wavelengths than white light does
why does light from a laser differ to light from a non laser
it is highly monochromatic
a laser is a convenient source of coherent light
what does it mean we can do if a light is monochromatic
we can specify its wavelength to within a nanometre
the wavelength depends on the type of laser that produces it
why is a laser damaging to the eye
the eye lens focuses the beam on a tiny spot on the retina and the intense concentration of light at that spot would destroy the retina
why are lasers coherent
photon s in the laser beam are inpahse with each other meaning they have the same constant phase difference
despite the difference in fringe separation what is the same about red and blue fringes
the central fringe of each pattern is in the same position on the screen
what do white light fringes show
each component colour of white light produces its own fringe pattern and each patten is centred on the screen at the same position
what happens as a result of all the fringes in white light being centred at the same position
the central fridge is white because every colour contributes at the centre of the pattern
