vovaalive.blogg.se

Wave optics contains all of ray optics, but the

If the wavelengths of the light become comparable to the dimensions of theĮquipment, then we study optical phenomena using the classical theory of radiation, or wave optics. So, as far as visible light is concerned, matter is quasi-continuous. Individual atoms in a solid are separated by distance on the order of 0.1 nm. So a laser beam with a diameter of 1 mm has a diameter of 2000 wavelengths. Wavelengths in the middle of the visible band are on the order of 500 nm. Consider the wavelength scale of light waves. Under these conditions we can make an approximation called In many situations, the wavelengths of the light being studied are very smallĬompared to the dimensions of the equipment used to study the light. Light is a transverse electromagnetic wave. In classical physics, we can classify optical phenomena into one of two categories: ray optics and wave optics. Now try some multiple choice questions on diffraction.Single slit diffraction Single slit diffraction Now look at the page on Diffraction Gratings Questions It can be shown theoretically that using light of wavelength, the width W c of the central fringe observed on a screen at distance D from the slit is given by: Using an adjustable slit, the observations show that making the slit narrower makes the fringes wider. Using different sources of monochromatic light in turn, the observations show that the greater the wavelength, the wider the fringes, The outer fringes are much less intense than the central fringe. The peak intensity of each fringe decreases with distance from the centre,Įach of the outer fringes is the same width, The central fringe is twice as wide as each of the outer fringes (measured from minimum to minimum intensity), The central fringe is twice as wide as the others. The intensity of the fringes is greatest at the centre of the central fringe. The pattern shows a central bright fringe with further dark and bright fringes either side. You see 'fringes' - bands of light (which from a laser are red) and no light (which on the diagram are shown in black. The diffracted light forms a pattern that can be observed on a white screen. These breaks are due to waves diffracted by adjacent sections on the gap being out of phase and cancelling each other out in certain directions.ĭiffraction of light by a single slit can be demonstrated by directing a parallel beam of light at the slit (a laser is good to use). This arrangement shows that the diffracted waves become more circular if:Ĭlose examination of the diffracted waves reveals that the each diffracted wavefront has breaks either side of the centre. Therefore, because a telescope is much wider than the eye pupil, much less diffraction occurs when using a telescope than when observing with the unaided eye.ĭiffraction of water waves through a gap can be observed using a ripple tank. This is partly because less diffraction occurs when waves pass through a wide gap than through a narrow gap.

This general property of all waves is very important in the design of optical instruments, such as cameras, microscopes and telescopes.įor example, when a telescope is used to observe planets, we can often see features that are not evident when observed directly. Particles would not do that so diffraction is evidence of the wave nature of light. A Level and AS level - UK KS 5 (Age 16 - 18)ĭiffraction is the spreading of waves when they pass through a gap or by an edge.GCSE and 'O' Level - UK KS4 (Age 14 - 16).