BIS 104 PQ 11 ans Spring 2010

BIS 104 PQ 11 ans Spring 2010 - optics d refractive index...

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BIS 104 PQ 11 ans Spring 2010 11. Define the following concepts or terms that are important aspects of microscopy: a) magnification: What is the formula for calculating the effective magnification of a microscope? Refers to the total increase in visible size of a specimen. It is the product of the magnification produced by the objective lens and ocular lens (total mag = ocular mag X obj lens mag) b) resolution: What is the formula for calculating the resolving power of a light microscope? d (resolution) = (o.61) (lamda nm) / (n) (sin alpha) The resolving power of a microscope is defined in terms of the ability to see two neighboring points in the visual field as two distinct entities. c) contrast: Refers to the visibility of a specimen, or the differences in appearance between adjacent parts of an object and its background. This can be achieved by modifying the specimen with stains and dyes or by modifying the optics of the microscope (e.g., phase-contrast
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Unformatted text preview: optics). d) refractive index: Refers to the degree to which a substance (air, glass, liquid) causes diffraction of light waves. Denoted as “n”, it is a unit-less value. E.g., refractive index of air = 1.0. e) numerical aperture (NA): What is the relationship between the NA of an objective lens and the useful magnification that can be obtained by that lens? Useful magnification is generally limited to approx 1,000 times that of the NA of that lens. A property of the objective lens. Defined as the product of the refractive index of the medium between the specimen and the objective lens and sin alpha (the light gathering ability of the lens). f) empty magnification: Refers to magnification beyond the resolving power of a microscope. It results in an increase in size of the image, but no increase or improvement in resolution or clarity of detail....
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