In this case, the size of the aperture is larger than the wavelength of the wavefront, the effect of diffraction is relatively small and the wavefront is curved only at the edges. In the case of a plane wavefront, if it is restricted by passing through an aperture, some of the wavelets forming the wavefront are removed, and hence the edges of the wavefront are curved. The construction of a circular wavefront is shown in Figure 3.įigure 3: Construction of a Circular Wavefront The tangent curve of the wavefronts produced by the secondary sources gives the new position of the original wavefront. He suggested that, at any instant, all points on a wavefront could be regarded as a secondary disturbance, giving rise to their own outward-spreading circular wavelets. This behaviour is explained by Huygens using the wave theory of light. When a single drop of water falls into a ripple tank, a circular wavefront will spread outwards from the disturbance. The greatest effect occurs when the wavelength is about the same size as the aperture.įigure 2: Diffraction at Different Size of Aperture It can be noted that the extent of the diffraction depends on the width of the gap compared with the wavelength. In Figure 2, diffraction is illustrated with two different sizes of aperture. The fact that light exhibits diffraction is a proof that light has wave properties. When light travels through an aperture or passes the edge of an obstacle, it deviates from the straight-line direction and appears to spread out. Diffraction of a light wave is illustrated in Figure 1.ĭiffraction may also occur at an edge. Diffraction is defined as the spreading of a wave into regions where it would not be seen if it moved only in straight lines after passing through a narrow slit or past an edge. This spreading out is called diffraction. When waves pass through a narrow gap, they spread out.
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