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# Chapter 6: 2D and 3D wavefronts

This chapter looks at different kinds of wavefronts. Learners should recall electromagnetic radiation from grade 10 as well as different wave properties from transverse waves and longitudinal waves. The following provides a summary of the topics covered in this chapter.

• Definition of a wavefront.

Wavefronts are imaginary lines joining waves that are in phase. A short activity in which learners join up the points in phase helps them to come to grips with what a wavefront is.

• Huygen's principle.

Every point of a wave front serves as a point source of spherical, secondary waves. After a time t, the new position of the wave front will be that of a surface tangent to the secondary waves. This principle describes how waves propagate and how waves interfere with other waves.

• Definition of diffraction.

Diffraction is the ability of a wave to spread out in wavefronts as the wave passes through a small aperture or around a sharp edge. This is most easily seen with water waves in a ripple tank. As the water waves reach the slit or barrier they spread out into the calm area beyond the slit or barrier.

• Sketching the diffraction pattern for a slit.

In this topic learners are shown how to make simple sketches of diffraction patterns as well as learning about how waves interfere to form crests and troughs.

• The degree of diffraction and calculating this.

The degree of diffraction is proportional to the wavelength and inversely proportional to the width of the slit. The degree of diffraction is explored in more detail and some simple calculations of this are given.

• Diffraction of light and how this relates to the wave nature of light.

All the above concepts are applied to how light diffracts when moving through a single slit. Light shone through a diffraction grating emphasises the wave nature of light.

It is important to note that this chapter contains a section on calculating the maxima and minima of diffraction. This topic is not in CAPs and is included for learners enrichment only. This topic should not be included in tests and exams.

## 6.1 Introduction (ESBND)

You have learnt about the basic properties of waves before, specifically about reflection and refraction. In this chapter, you will learn about phenomena that arise with waves in two and three dimensions: diffraction. We will also build on interference which you have learnt about previously but now in more than one dimension.