L12: Diffraction

first rule for huygens principle

each point on a wave front is the source of a spherical wavelet that spreads out at the wave speed

2nd rule of huygens principle

shape of the wavefront is the line tangent to all the wavelets

huygens principle assumption

any point beyond the wavefront is a superposition of all these wavelets taking into account both amplitue and direction

how is a shadow formed

wavefront is incident on a corner of an obstacle

light being diffracted procues?

pattern of light that produces maxima and minima due to interference of slit

the smaller the slit width relative to wavelength?

the greater the diffraction

what diffracts better, red or blue light

red light

greater wavelength leads to greater or lower defraction?

greater

describe fresenel wavfront

curved wavefront

describe fraunhoffer wavefront

plane wavefront

resolution

two small objects at a large distance being viewed through a circular aperture, each source gives rise to a diffraction pattern

what is rayleighs criterion

two objects or point sources are deemed to be resolve if the central maximum of one pattern falls on the first minimum of the other pattern

if the images are formed on 2 neighbouring cones

they will not be resolved as two seperate sources

if there is one unstimulated cone between those on which the images are formed, then the?

two sources may be perceived as being seperate

seperation of stimulated cones must be?

4 um

airy disc

bright, circular pattern that appears when light passes through a small circular opening, such as a telescope or microscope, and diffracts

two seperate point sources =

airy disc

if airy discs are well seperated, they will be resolved serperatly as

two distinct points

when does interference occur

when 2 waves travel at different distances to each other