First, look at how spatial variations in displacement produce compression or expansion and thus derive how the pressure depends on displacement.(We might picture a wave travelling through a pipe, and neglect the viscous and thermal interactions at the wall.) Here’s what we shall do to analyse sound propagation: We’ll consider a section with cross section A.
Let’s consider a one dimensional wave travelling in the x direction. The wave we analyse here is sound in an elastic medium, such as air. When analysing a longitudinal wave, we still use y for the displacement, but remember that this displacement is in the x direction. In a longitudinal wave, displacements are parallel to the direction of the wave. When we analysed a transverse wave (that in a string), we used y as the displacement for a wave travelling in the x direction. The wave equation and the speed of sound.Newton’s laws: how pressure variations produce displacements.Compression: how displacement affects pressure.Why an opaque object has a particular colour. The effect of viewing objects through filters or the effect on light of passing through filters How the colour of an object is related to the differential absorption, transmission and reflection of different wavelengths of light by the object Objects that transmit light are either transparent or translucent. If all wavelengths are absorbed the objects appears black. If all wavelengths are reflected equally the object appears white. Wavelengths that are not reflected are absorbed. The colour of an opaque object is determined by which wavelengths of light are more strongly reflected. Reflection from a rough surface causes scattering: this is called diffuse reflection.Ĭolour filters work by absorbing certain wavelengths (and colour) and transmitting other wavelengths (and colour). Reflection from a smooth surface in a single direction is called specular reflection. Students should be able to use wave front diagrams to explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium.Įach colour within the visible light spectrum has its own narrow band of wavelength and frequency. Students should be able to construct ray diagrams to illustrate the refraction of a wave at the boundary between two different media. Some effects, for example refraction, are due to the difference in velocity of the waves in different substances. Students should be able to describe the effects of reflection, transmission and absorption of waves at material interfaces.ĭifferent substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength. Students should be able to construct ray diagrams to illustrate the reflection of a wave at a surface. Waves can be absorbed or transmitted at the boundary between two different materials. Waves can be reflected at the boundary between two different materials. Students should be able to show how changes in velocity, frequency and wavelength, in transmission of sound waves from one medium to another, are inter-related. Identify amplitude and wavelength from given diagramsĭescribe a method to measure the speed of sound waves in airĭescribe a method to measure the speed of ripples on a water surface. The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium.Īll waves obey the wave equation: wave speed = frequency× wavelength ( v = f λ) The frequency of a wave is the number of waves passing a point each second. The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave. The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position. Students should be able to describe wave motion in terms of their amplitude, wavelength, frequency and period. Students should be able to describe evidence that, for both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels. Students should be able to describe the difference between longitudinal and transverse waves. Sound waves travelling through air are longitudinal. Longitudinal waves show areas of compression and rarefaction. The ripples on a water surface are an example of a transverse wave. Waves may be either transverse or longitudinal. Back to Teaching Rota Year 9 Wave Properties Objectives
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