Diffraction Flashcards
What happens to waves as they pass a narrow gap, (aperture)?
They spread out.
When the aperture is much bigger than wavelength, how much diffraction is there?
Barely noticeable amounts.
When aperture length is a number of wavelengths wide, how much diffraction is there?
An increased amount compared to diffraction with a smaller wavelength.
When aperture length is same to the wavelength, how much diffraction is there?
Maximum.
How does diffraction for sound and light compare in doorways?
For sound, it is easy to hear sound from an open doorway as the wavelength and aperture size are roughly the same, whereas light has a wavelength a hundred million times smaller than the gap, so diffraction for light is significantly less, and it will be harder to see people out of the line of sight.
How does diffraction occur in obstacles blocking path movement?
Diffraction occurs around the edges of the obstacle, and a shadow is created where the wave is blocked. The wider the obstacle compared to wavelength, the less diffraction, and so greater shadow.
Describe how Young Slits is used to create fringes.
If wavelength of a light wave is similar to aperture size, a diffraction pattern is made with a bright central fringe of highest incident photons per unit area, being most intense. The narrow the slit, the wider the diffraction pattern. Coherent light is needed.
How is the maxima fringe created?
At the central maximum all light travels in a straight line at the same distance, and so they move in phase, and their amplitudes add to create a resultant.
How are the smaller bright fringes created?
Constant phase difference makes a smaller resultant force, creating the shape of a moon, for instance.
How are the dark fringes created?
Dark fringes occur where phase difference makes phasors form a loop with zero resultant.
