Diffraction Flashcards
What is a wavefront?
an imaginary line that cuts the waves, joining up points that are in phase with each other
What is diffraction?
when a wave passes through an obstacle or goes into a gap it spreads out and changes shape
What wave properties change during diffraction?
none, frequency wavelength and wavespeed remain the same
What does narrowing the gap do to a wave passing through it?
the wavefronts become more circular - there is more diffraction and hence more spreading
when do we get the most diffraction?
when the gap is 1 wavelength long of the wave passing through it
What happens when the gap is too small?
the wave is reflected back
What does diffraction depend upon?
the wavelength and width of gap (in comparison)
When does diffraction become more noticeable?
as the gap is decreased to the magnitude of the wavelength of the wave
How can we investigate diffraction?
an oscillating paddle generating waves with paralllel wavefronts in water. we also have an object in the ripple tank which acts as an obstacle
Is diffraction noticeable with a huge gap?
no
What is HUYGEN’S CONSTRUCTION?
it states that every point on a wavefront may be considered to be a source of secondary wavelets that spread out in the forward direction at the speed of the wav. The every wavefront is an envelope of secondary wavelets
What happens when an obstacle stands in front of a wave?
we get diffraction around it but behind we get an area wth a shadow, as waves don’t combine straight away
How can we make the shadow longer?
by increasing object width compared to wavelength to cause less diffraction
What interference pattern do we get when white light is passed through a single slit, with the slit having a similar width to the wavelength
consecutive bright and dark fringes.
- this pattern has a central bright fringe with alternating bright and dark fringes either side
- dark fringe is a minima
- bright fringe is a maxima
- intensity decreases the further a fringe is from the central maxima
What does diffraction of light through more slits cause?
narrower maxima and minimas but of greater intensity, this is because the pattern is reinforced
Why does having narrower maximas and minimas help (PAPER 3)?
increased precision of measurements decreasing uncertainty -
What is a diffraction grating?
surface with loads of parallel gaps
Why are maximas produced?
when coherent waves superpose causing constructive interference. The waves arriving at the point of the maxima must be in phase.
Why are minimas produced
when coherent waves superpose causing destructive interference. The waves arriving at this point must be out of phase
Equation for maximum amount of orders?
D/lambda = max orders
Equation for diffraction?
n(lambda) = dsinx where n = order lamdba = wavelength d = slit seperation or slit width sinx = spread
How can we create sources of coherent light?
passing it through a single slit
Larger wavelength means…
more spread
greater slit seperation means…
less spread
What happens when we use white light with a diffraction grating?
since white light is a mixture of colours we get a spectra pattern. Each order in the pattern becomes a spectrum, with red on the outside and violet on the inside. The zero order maximum is just white as all wavelengths just pass straight through.
monochromatic light?
light of one singular wavelength
