waves- interference an diffraction Flashcards
what is diffraction
the way waves spread out as they come through a narrow gap or go round obstacles.
all waves diffract
what does the amount of diffraction depend on
the wavelength of the wave compared with the size of the gap
when do you get the most diffraction
when the gap is the same size as the wavelength
what does the light need to be so form a diffraction grating when shone through a slit
monochromatic and coherent
what is monochromatic light
the light all has the same wavelength and frequency and so is the same colour
what does coherent mean
phase difference is constant and same frequency and wavelength
what do you see when a laser is shone through a slit
a central fridge called the central maximum with bright and dark fringes alternating on either side caused by destructive and constructive interference
what happens when white light is shone through a slit
since white light is made up of a mixture of colours with different wavelengths the different wavelengths or colours are diffracted by different amounts resulting in a spectra of colours produced. it also gives a wider maxima and a less intense diffraction pattern with a central white fridge and they a spectra with violet closet to the centre maxima and red the furthest
what is the central maximum
the brightest part of the pattern this is because the intensity is the highest in the centre
intensity
power per unit area
what happens to the central maxima when you increase the intensity
for monochromatic light all the photos have the same energy so by increasing the intensity you are increasing the number of photos per second so more photos per unit area hitting the central maximum per second
what are the two things that effect the width of the central maximum
1- increasing the slit width decreased the diffraction making the central maximum narrower and so the intensity of the central maximum is higher
2- increasing the wavelength increases the amount of diffraction and so the central maximum get wider and the intensity is lower
what is a easy way of demonstrating two source interference
with water or sound as they have good sided wavelengths too measure. you just need to make sure the sources are coherent
what is young’s double slit experiment
a practical to see two source interreference with light by shining a single light source through two slits creating two coherent light sources. getting a pattern of light and ark fridges depending on the type of interference
who was the first person to do the double slit experiment
Thomas young came up with the equation to work out the wavelength from this experiment
what must you make sure you do when working with lasers
never shine towards a person
have warning sighn up
turn of when not used
how else can you do he double slit experiment other then with a laser
microwaves and a probe
what do the different letters in the double slit experiment formular mean
w= fridge spacing
lander= wavelength
s= spacing between slits
D= distance between screen and slits
how did the young’s double slit experiment provide evidence that light is a wave
it showed light could both diffract and interfere which proved EM radiation must act as a wave which proved that light was not formed of tiny particles which was what was initially believed
path difference
the difference in the distance travelled by two waves.
how could you convert light from a light bulb into monochromatic coherent light source
place a single slit to make the light have the same path difference and a filter to make it monochromatic.
what happens when the gap is the same size as the wavelength
most of the waves are reflected
what happens when the gap is larger then the wavelength
there is less noticeable diffraction
what happens when you shine monochromatic light through a single slit
the light will diffract forming and interference pattern of light and dark fringes. the bright central fridge is double the width of the other fringes and the fridges intensity decreases form the middle
what causes constructive interreference
when two waves meet in phase
what causes destructive interference
the waves arrive completely out of phase
what is a diffraction grating
a slide containing equally spaced slits very close together
if two waves produce a light fridge what must be their phase difference
one wave
how is a central maxima produced from a diffraction grating
then the beams passes through the grating it is split up into different beams that all refract out of the grating when the waves arrive in phase at the screen they constructively interfere producing an central maxima
