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Define absolute refractive index. Absolute refractive indices of medium ‘A’ and medium ‘B’ are and ‘nb’ respectively, what is the refractive index of medium ‘B’ with respect to medium ‘A’? How does the velocity of light vary with change in the optical density of the media? |
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Answer» Absolute refractive index of a medium is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the medium. If c is the velocity of light in vacuum and v in the medium, then: n = c/v Absolute refractive index = Speed of light in vacuum /Speed of light in medium According to question, For B, Dividing (ii) by (i), nb /na=Speed of light in medium A/Speed of light in medium B Now, refractive index of medium 'B' with respect to medium 'A=Speed of light in medium A/Speed of light in medium B = nb/na = b/a Optical density of a medium is the measure of its transmittance for a radiation of particular wavelength. Higher is the value of optical density, lower is transmittance. it is expressed as log10 (1/T), where T is the transmittance in percentage (T = I/10). And also a higher value of refractive index means higher optical density. This means that light travels slower, in a medium with high optical density. Speed of light slows down in a optically denser because light interacts with the matter inside the denser medium. |
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