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Forensic Science SCI183 Ch7 docx

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Ryerson University
CHY 183
Raji Iyer

Chapter 7: The Microscope Key Terms Binocular:  Describes a microscope with two eyepieces Condenser  The lens system under the microscope stage that focuses light onto the specimen Depth of Focus  The thickness of a specimen that is entirely in focus under a microscope  Higher magnification has lower depth of focus Eyepiece Lens  The lens of a microscope into which the viewer looks; same as the ocular lens Field of View  The area of the specimen that can be seen after it is magnified Microspectromphotometer  An instrument that links a microscope to a spectrophotometer Monocular  Describes a microscope with one eyepiece Objective Lens  The lower lens of a microscope, which is positioned directly over the specimen Parfocal  Describes a microscope such that when an image is focused with one objective in position, the other objective can be rotated into place and the field will remain in focus Polarized Light  Light confined to a single plane of vibration  Light that is confined to a single plane of vibration is said to be plane- polarized Polarizer  A device that permits the passage of light waves vibrating in only one plane Real Image  An image formed by the actual convergence of light rays on a screen Transmitted Illumination  Light that passes up from the condenser and through the specimen Vertical or Reflected Illumination  Illumination of a specimen from above; in microscopy it is used to examine opaque specimens Virtual Image  An image that cannot be seen directly. It can be seen only by a viewer looking through a lens Key Points  The maximum useful magnification of a compound microscope is approximately 1,000 times the numerical aperture of the objective being used  In its usual mode, the scanning electron microscope (SEM) has a magnification that ranges from 10x to 100,000x  If an eyepiece lens with a magnification of 10x is combined with a 45x objective, the respective magnification will be 450 x  The polarizing microscope has found wide application for the examination of birefringent materials present in soil?  A scanning electron microscope can be used to determine whether or not a suspect has recently fired a gun  The “fingerprint” IR spectrum can be seen using a microspectromphotometer Essay Questions 1. Compare and contrast the comparison microscope to the compound microscope. 2. Describe how a microspectrometer is used to examine trace evidence Introduction • A microscope is an optical instrument that uses a lens or a combination of lenses to magnify and resolve the fine details of an object • The magnified image seen by looking through a lens is know an a virtual image • An image viewed directly is known as a real image • The object to be magnified is placed under the lower lens called the objective and is viewed through the upper lens, called the eye-piece The Compound Microscope  In the basic compound microscope, the object to be magnified is placed under the lower lens (objective lens) and the magnified image is viewed through the upper lens (eyepiece lens).  The magnification of the image can be calculated by multiplying the magnifying power of the objective lens times the magnifying power of the eyepiece lens.  The microscope is composed of a mechanical system which supports the microscope, and an optical system which illuminates the object under investigatio
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