Ch.5 OPTICS Flashcards
why is the central maximum have the most photons
In monochromatic light, all the photons have the same energy, so an increase in the intensity means an increase in the number of photons per second
sooooo more photons per unit area hitting the central maximum per second than other bright fringes
what are the two things that affect the width of the central maximum
- increasing SLIT width DECREASED the amount of diffraction sooo central maximum is NARROWER and intensity of central maximum is HIGHER
- increasing the WAVELENGTH increases the amount of diffraction sooo central maximum is WIDER and interrupt of central maximum is LOWER
what does diffraction depend on
it depends on the wavelength of wave compared to the size of slit
if gap is a lot bigger than wavelength then diffraction isn’t noticeable
you get the most diffraction when the gap is the same size as the wavelength
if gap is smaller than wavelength then waves are mostly reflected back
why is laser light used for the slit experiment
laser light is monochromatic so this provides a clearer pattern than non monochromatic light as diff wavelengths diffract diff amounts
why can a student hear a bell alarm but not see it and he’s in another room
the wavelength of sound waves and the size of the doorway should be around the same length for maximum diffraction.
sound waves will diffract completely allowing the student to hear
the wavelength of light waves are much smaller than size of doorway so diffraction is unnoticeable therefore not letting the person see it
what happens when student uses narrow slit means
the central maximum will be wider and less intense and using narrower slit means more diffraction and so there will be fewer photons per unit area so intensity will be lower
for the white light grating which colour is on the outside and which is on the inside
red on the outside and violet on the inside
what is used to discover the structure of the DNA
X- ray crystallography
X-ray wavelengths is of similar scale to spacing between atoms in crystalline solids sooooo X-rays will form diffraction patterns when directed at a thin crystal
why does light go faster in a vacuum
it slows down in other materials because it interacts with the particles in them
the more dense the slower it gets
what happens when incidence angle is equal to critical angle
then it will be refracted against the boundary so 90 degrees
what happens when critical angle is less than incidence angle
then material will fully reflect causing an TIR
what is step index optical fibre
they have high refractive index and are surrounded by CLADDING with a lower refractive index to allow total internal reflection
cladding also protects the fibre from scratches which could lead to light escaping
light is shown at one end of fibre and fibre is narrow so that light always hits the boundary between fibre and cladding at an angle bigger than critical angle
so all light is TIRed from boundary to boundary until reaches other end
what causes signal degradation
absorption or by dispersion which causes info to be lost
what is Absorbtion
it causes loss of amplitude
as the signal travels some of its energy is lost through absorption by the material the fibre is made from. this energy loss results in the amplitude of the signal being reduced
what does dispersion do
it causes pulse broadening
there’s two types of dispersion
1. model dispersion : light rays enter fibre at diff angles and so take diff paths
this rays which take a longer path take longer to reach the other end then those that travel down the middle of the fibre
- material dispersion : light consists of diff wavelengths that travel at diff speeds in the fibre so this causes some light wavelengths to reach the end of the fibre faster than others.
both lead to pulse broadening as the signal sent down the fibre is broader at the other end
broadening pulses can overlap each other and confuse signal
