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To deduce the wave nature of light, explain its behavior when it interacts with material obstacles (diffraction) or its behavior when light from two coherent sources interfere with each other (interference), we need to explain what are waves and what are their properties (wavelength, frequency, mathematical relationship between wavelength and frequency, superposition principle, ?). Two principal approaches are generally used to introduce waves: 1/ An experimental approach (the example commonly used approach): to observe the water waves pattern obtained when drops of water (with an eye dropper, two eye droppers, or equivalent) fall -at a steady rate- on a calm pool of water surface. 2/ A theoretical approach: Wave coming from one source is represented by a sinusoidal function; Superposition of waves coming from two coherent sources is done by a sum of two sinusoidal functions with constant phase difference. In Tunisia, different workshops on “wave nature of light based on interference and diffraction” using Active Learning process have been organized for about 150 secondary school teachers in 2009. These workshops are based on UNESCO Active Learning in Optics and Photonics (ALOP) project. This paper will show how taking water wave's pattern using some participant's mobile camera helps to make some misconceptions resolved and includes at the same time other more complex phenomena. |
