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Unformatted text preview: INDIANA UNIVERSITY, DEPARTMENT OF PHYSICS, P309 LABORATORY Laboratory #28: Refraction and Dispersion Goal: Learn about refraction of visible light in liquids, understand the principle of an AbbØ refractometer and measure the refractive index and the dispersion of liquid media. Equipment: Abb ė refractometer, standard glass gauge block, bromo-naphtalene, NaCl, sugar, scale, cleaning equipment (A) What is refraction and dispersion? Light passing from vacuum to some transparent medium is refracted because the speed of light in the medium is less than in vacuum. The ratio of the two velocities is called the &Index of Refraction¡ n . Consider light that passes from one medium ( n 1 ) to another ( n 2 ). When the second medium is optically denser than the first ( n 1 < n 2 ), the light is bent towards the normal to the interface. Snell¡s law relates the incident angle α , the angle of refraction β and the two indices of refraction sin α / sin β = n 2 / n 1 . (1) The index of refraction depends on the wavelength λ of the light. The index of refraction is usually evaluated at an intermediate wavelength λ D =589.2nm (yellow). The dependence on wavelength is called dispersion . The magnitude of dispersion, D FC , is usually defined as the difference of the indices of refraction measured at the two standard wavelengths λ F =486.1nm (blue) and λ C =656.3nm (red) 1 . C F FC n n D − = , (2) but often an alternative definition, called &AbbØ¡s number¡ is used (for more details, see a textbook on optics, e.g., ref.[MEY]) C F D n n n − −...
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- Spring '11
- Light, Index of Refraction, refractive index