Gujarat BoardEnglish MediumSTD 12 SciencePhysicsWAVE OPTICS2 Marks
Question
Briefly discuss different theories (or models) about light given by different scientists.
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Answer
→Many different theories are given by different scientists about the fundamental nature of light, which are as follows : • Descartes : →In 1637, Descartes gave the corpuscular model of light and derived Snell's law. It explained the laws of reflection and refraction of light at an interface. The Corpuscular model predicted that if the ray of light (on refraction) bends towards the normal, then the speed of light would be greater in the second medium. • Isaac Newton : →The Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of tremendous popularity of this book, the Corpuscular model is often attributed to Newton. →The wave theory of Huygens was not readily accepted primarily because of Newton's authority and also because, light could travel through vacuum and it was felt (or believed) that a wave would always require a medium to propogate from one point to the other. • Huygens : →In 1678, the Dutch physicist Christian Huygens put forward the wave theory of light. →This wave model could satisfactorily explain the phenomenon of reflection and refraction. The model predicted that on refraction, if the wave bends towards the normal, then the speed of light would be less in the second medium. This is in contradiction to the prediction made by using the Corpuscular theory (Corpuscular model of light.) It was later confirmed by experiments and it was shown that the speed of light in water is less than the speed in air. • Foucault : →He carried out an experiment in 1850 and confirmed by experiment and showed that the speed of light in water is less than the speed in air as per prediction of the wave model. • Thomas Young : →He performed his famous interference experiment in 1801 and it was firmly established that light is actually (indeed) a wave phenomenon. The wavelength of the visible light was measured and found to be extremely small. For example, the wave length of the yellow light is about $0.6 \mu m$. Because of the smallness of the wavelength of the visible light (in comparison to the dimensions of typical mirrors and lenses), light can be assumed to approximately travel in straight lines.
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