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The refractometer is used to help identify gem materials by measuring their refractive index, one of the principal properties used in determining the type of a gemstone. Due to the dependence of the refractive index on the wavelength of the light used ( i.e. dispersion ), the measurement is normally taken at the wavelength of the sodium line D ...
Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting surfaces.
For a thin prism, the deviation of violet light, is and that of red light, is (). The difference in the deviation between red and violet light, ( δ v − δ r ) = ( n v − n r ) A {\displaystyle (\delta _{v}-\delta _{r})=(n_{v}-n_{r})A} is called the Angular Dispersion produced by the prism.
Astigmatism may be corrected with eyeglasses, contact lenses, or refractive surgery. Various considerations involving ocular health, refractive status, and lifestyle frequently determine whether one option may be better than another.