KCL Section 2: Huygen’s construction (Waves and Photons) Flashcards
What is diffraction?
Diffraction is when a wave is spread out as a result of passing through a gap or past an obstacle.
What is Huygen’s construction?
Huygens suggested that the new waves, formed at the wavefront, would be spherical and travel at the same speed and wavelength as the original wave.
It can be used to explain diffraction.
What does Huygen’s construction prove?
Huygen’s construction can also be used to explain the change of angle at a boundary (refraction).
It can be used to explain diffraction.
If the gap is bigger than the wavelength then the central part of the wavefront will _______ _____________, but the edges will _____.
If the gap is bigger than the wavelength then the central part of the wavefront will continue ‘un-diffracted’, but the edges will curve.
What is X-ray crystallography
The separation between molecules in a crystal can diffract xrays.
The diffraction pattern created can be analysed to determine the spacing and arrangement of the atoms causing it.
What has X-ray crystallography been used for?
Rosalind Franklin and Raymond Gosling used x-ray crystallography to image DNA in 1952. Both James Watson and Francis Crick were struck by the simplicity and symmetry of this pattern. The distinctive “X” in this X-ray photo is the expected pattern of a helix. Because the X-ray pattern is so regular, the dimensions of the helix must also be consistent.
What is the resolution of a detector?
The resolution of a detector (eye, telescope) is the smallest separation two objects can have to still be distinguished separately.
How can a change in aperture affect resolution?
Diffraction caused by the aperture increases as the aperture decreases - the iris of the eye has a smaller aperture, so the resolution is lower than with a telescope.
