InterviewSolution
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InterviewSolution
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Swarali has got the following observations while doing an experiment. Answer her questions with the help of observations.Swarali observed that the light bent away from the normal, while travelling from a denser medium to a rarer medium. When Swarali increased the values of the angle of incidence (i). the values of the angle of refraction (r) went on increasing. But at a certain angle of incidence, the light rays returned into the denser medium.So, Swarali has some questions. Answer them.(a) Name this certain value of i. What is the value of r at that time? (b) Name this process of returning light in the denser medium. Explain the process. |
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Answer» (a) Critical angle r = 90° (b) Total internal reflection. As light goes from a denser to rarer medium, if the value of the angle of incidence increases, then the value of the angle of refraction also increases. But after a specific angle of incidence called the critical angle, the light gets reflected back into the denser medium. The ray of light incident at the boundary separating the two media bends away from the normal on refraction. Here, the angle of refraction r, is greater than the angle of incidence i. Now anw = \(\frac{sin\,i}{sin\,r}\) < 1. Here, anw is the refractive index of sin r air with respect to water. As anw is constant, r increases as i increases. For r = 90°, the ray travels long the boundary. If i is increased further, as r cannot be greater than 90°, light does not enter air. There is no refraction of light and all the light enters water on reflection. This is called total internal reflection. For r = 90°, anw = \(\frac{sin\,i}{sin\,90^\circ}\) = sin i. This angle i is sin 90° called the critical angle. |
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