5.6- DIFFRACTION Flashcards
What is diffraction?
spreading of waves when they pass through gap or by edge
What is the general property of diffraction of all waves very important in?
design of optical instruments, i.e. cameras, microscopes + telescopes
What is partly the reason for why we can see features that are not evident when observed directly when looking at planted through a telescope?
partly as less diffraction occurs when waves pass through wide gap than through narrow gap
What can diffraction of water waves through a gap be observed by using?
ripple tank
What does the ripple tank arrangement show about how diffracted waves will spread out more if…? (2)
gap made narrower, or
wavelength made larger
What should close examination of the diffracted wave from the ripple tank arrangement reveal?
each diffracted wavefront has breaks either side of centre
What are the breaks at either side of the centre of the diffracted waves from the ripple tank arrangement due to?
waves diffracted by adjacent sections on gap being out of phase + cancelling each other out in certain directions
What can diffraction of light by a single slit be demonstrated by?
directing parallel beam of light at slit
What does the diffracted light form? (diffraction of light by a single slit)
pattern that can be observed on white screen
What does the pattern formed by the diffracted light show? (diffraction of light by a single slit)
shows central fringe with further fringes either side of central fringe
Where is the intensity of the fringes the greatest? (diffraction of light by a single slit)
at the centre of the central fringe
What is the width of the central fringe in comparison to the outer fringes? (diffraction of light by a single slit)
central fringe twice as wide as each of the outer fringes (measured from minimum to minimum intensity)
What does the peak intensity of each fringe decrease with? (diffraction of light by a single slit)
distance from the centre
How is each of the outer fringes similar? (diffraction of light by a single slit)
each of the outer fringes is same width
What is the intensity of the outer fringes like in comparison to the central fringes?
outer fringes much less intense than central fringes
What does the observations show when a single slit pattern is observed using different sources of monochromatic light in turn?
greater the wavelength, the wider the fringes
What does the observations show when a single slit pattern is observed using an adjustable slit?
making slit narrower makes fringes wider
Equation for the width of the central fringe
W = λ/a * 2D
λ- wavelength of light
a- width of single slit
D- distance from screen to slit
What is the width of each fringe proportional to?
λ/a
What does the width of each fringe being proportional to λ/a show?
fringes narrower using blue light than if red light had been used
In the double slit experiment, where does light pass through and what does it produce?
passes through two slits of double slit arrangement + produces interference pattern
What happens if the slits are too wide and too far apart in the double slit experiment?
no interference pattern observed
Why is no interference pattern is observed when the slits is too wide and too far apart in the double slit experiment?
interference can only occur if light from two slits overlap
How must the slits be in the double slit experiment for interference to happen? (2)
each slit must be narrow enough to make light passing through it diffract sufficiently
two slits must be close enough so diffracted waves overlap on screen
Equation for fringe spacing of interference fringes?
w = λD/s
Equation for width of central diffraction fringe?
W = 2λD / a
