Transverse waves and light

The diffraction grating

The diffraction grating Young’s demonstration of the wave nature of light was the prelude to further experimental and theoretical work on the subject which continued during the nineteenth century. Within a few years, the German physicist, Joseph von Fraunhofer, invented a more satisfactory w~y of measuring the wavelength of light. Instead of two slits, he used as many close …

Fringes formed by white light

Fringes formed by white light Broadly speaking, white light consists of seven different colours, as we saw in chapter 025. So if a white light source is used in Young’s experiment we get seven sets of differently spaced coloured fringes all superimposed on one another. The previous experiment shows that the central fringes for each colour are …

Wavelength and colour

Wavelength and colour The colour of light is related to the frequency and therefore to the wavelength of the light waves if they are passing through the same medium. The wavelength increases as we go from violet towards the red end of the spectrum. The wavelength of red light is approximately twice that of violet. Returning to Young’s …

Measurement of wavelength from Young’s experiment

Measurement of wavelength from Young’s experiment Fig. 26.14 shows the ray geometry for the first bright fringe next to the central one. For clarity the vertical scale of this diagram has, like the others, been greatly exaggerated: actually the fringe spacing x is only about one six-hundredth of the distance D. We saw in the previous section that …

Production of interference fringes using Young’s slits

Production of interference fringes using Young’s slits Fig. 26.12 shows the general scheme of a modern version of Young’s experiment. Two very narrow, close, and parallel slits S 1 and S2 are illuminated by the light from a single slit S parallel to them, and placed in front of a strong monochromatic (= one colour or wavelength) light …

Ray geometry of Young’s experiment

Ray geometry of Young’s experiment In Fig. 26.13 all light waves leave Sl and S2 in the same phase, and the rays give the directions of the wave paths. If we consider a point C on the perpendicular bisector of SIS 2′ the waves travelling along the rays SIC and S2C have travelled equal distances. Hence they …

How the wave nature of light was first discovered

How the wave nature of light was first discovered If we imagine that the two water wave sources of Fig. 26.11 to be replaced by twopoint light sources then, if light is a form of wave motion, we should expect similar constructive and destructive interference to occur. In other words we ought to get increased brightness along …

Interference

Interference When two ball-ended dippers are attached to the vibrator of the ripple tank, two sets of circular ripples are sent out which pass through one another as shown in Fig. 26.10. Where the two waves are superposed in the same phase, e.g., crest on crest, we get lines of increased disturbance or constructive interference. These are …

Diffraction

Diffraction Interesting and unexpected results are obtained when straight waves are incident on an opening formed between two vertical metal barriers placed in the ripple tank. If the opening is a wide one compared with the wavelength of the waves, they will pass through in parallel straight lines, though we cannot fail to notice a slight bending round at …

Refraction of waves at curved boundaries

Refraction of waves at curved boundaries When carrying out experiments on refraction, using very shallow water, it will be found that a very slight trace of detergent in the water will improve the results by reducing surface tension effects. The wave-focusing action of a shallow lens-shaped patch of water may be studied by placing a bi-convex piece of perspex …