5.6 Diffraction Flashcards
what is diffraction
the s[reading of waves when they pass around an object or through a gap or by an edge
what was diffraction important for inventing
the design of optical instruments
how does a telescope use diffraction
less diffraction occurs when waves pass through a wide gap than a narrow gap.
therefore because the telescope is much wider than the eye pupil much less diffraction occurs
when do diffracted waves in a ripple tank spread out more
when the gap is made narrower
when the wavelength is made larger
why in a ripple tank does each diffracted wavefront break either side of the centre
due to waves diffracted by adjacent sections on the gap being out of phase and cancelling each other out in certain directions
what does diffraction of light by a single slit show
forms a pattern that can observed on a white screen.
shows a central fringe with further fringes each side of the central fringe
where is the intensity of the fringes the greatest
at the centre of the central fringe
the further away from the central fringe the weaker the intensity becomes
how large is the central fringe
twice the size as the cute fringes
it is measured from minimum intensity to minimum intensity
how wide are the outer fringes
there all the same width and are much less intense that the central fringe
intensity decreases the further away you get
what makes the fringes wider when doing single slit diffraction
the greater the wave length the wider the fringes
making the slit more narrow widens the fringes
how do you measure the width of the central fringe
w = wavelength/ width of single slit (a) x. x 2d
d= distances from screen to slit
what happens in double slit diffraction if the slits are too wide or too far apart
no interference pattern is observed
because interference can only occur if the light from 2 slits overlap
what must be insured in order for an interference pattern to be shown
each slit must be narrow enough to make the light passing through it diffract sufficiently
the two slits must be close enough so the diffracted waves overlap on the screen
fringe spacing of the interference fringes equation for double slit diffraction
w = lambda d / s
s= separating between the centre of both slits
width of central diffraction fringe for double slit diffraction
w = 2 lambda d / a
a = width of the slits
