If you shine a laser pointer from air into a denser medium (like glass or water), the beam is bent – as shown in the picture above. This bending of light, as it passes from one medium to another, is called refraction. It’s easy to see refraction using a laser pointer because it produces a… Continue reading 19.21 Refraction

In post 19.9, I wrote that light and other forms of electromagnetic radiation, are propagated as waves. What is the evidence for this statement? In the picture above, water waves (blue) on the sea, meet the entrance to a harbour that is protected by walls (black). The walls prevent the waves from entering the harbour… Continue reading 19.20 Diffraction – light is propagated as waves

Before you read this, I suggest that you read post 19.9. We know that hot objects can emit electromagnetic radiation because sometimes they are “red hot”; then they emit red light – a form of electromagnetic radiation (post 19.9). The wavelength of emitted radiation shifts to shorter wavelengths (longer frequencies, post 19.9) as the temperature… Continue reading 19.19 Radiation of heat

Before you read this, I suggest you read post 16.35. In post 16.34 we saw that heat flows spontaneously from hot things to cold things – this leads to the idea of entropy that was discussed in more detail in posts 16.35 and 16.38. Conduction (post 19.14) is one mechanism for the flow of heat.… Continue reading 19.18 Convection of heat

Before you read this, I suggest you read the first 8 paragraphs of post 18.6. In previous posts, we have seen how differential equations (post 19.10) can be used to represent diffusion (post 19.15), the conduction of heat (post 19.15) and the behaviour of waves (post 19.12). We also saw how a differential equation could… Continue reading 19.17 Computer modelling – the simple harmonic oscillator

Before you read this, I suggest you read posts 18.26 and 19.15. In post 18.26, we saw that particles that are free to move in a medium (like molecules in a solution) will spontaneously spread to achieve an even concentration; this process is called diffusion. In post 19.15, we saw that, for diffusion in one… Continue reading 19.16 Solution of the diffusion equation

Before you read this, I suggest you read post 19.14. In post 19.12, we saw how a wave could be represented, in time and space, by the wave equation. The concentration of a diffusing substance also varies in both space and time (post 18.26). Can we represent this dependence by a differential equation too? In… Continue reading 19.15 The diffusion equation

Before you read this, I suggest you read post 18.26. In post 18.26 we saw that molecules (or atoms or ions) move spontaneously from regions of high concentration to regions of low concentration, in order to increase the entropy of the system. Processes that increase entropy occur spontaneously because they lead to a more probable… Continue reading 19.14 Fick’s law of diffusion and the conduction of heat

In post 18.12 I introduced the idea of a standing wave as a vibration that could exist on a string tethered at both its ends. In the picture above, a string of length L is tethered at both ends, A and B. The fundamental wave (shown in red) then has its greatest amplitude of vibration… Continue reading 19.13 More about standing waves: intuition and analysis

Before you read this, I suggest you read posts 19.10 and 19.11. I introduced the idea of a wave in post 18.10 but, if you think about it, you will see that in that post and later posts (18.11, 18.12, 18.13, 18.14, 19.9) on waves, I have never defined exactly what I mean by the… Continue reading 19.12 The wave equation