LABORATORY REPORT EXERCISE 3 Phase Contrast Microscopy A. Short Answer Questions
ID: 82875 • Letter: L
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LABORATORY REPORT EXERCISE 3 Phase Contrast Microscopy A. Short Answer Questions 1. Staining of cells is often performed to enhance images acquired by brightfield microscopy. Phase- contrast microscopy does not require cell staining. Why is this advantageous? 2. light passes through a transparent object, bow are direct and diffracted light rays produced? How much phase shift occurs? 3. How do coincidence and interference of light rays differ? What type of image does each produce? How does that contribute to a sharper image? 4. Differentiate between bright- phase and dark-phase microscopy in terms of phase shift 5. Which two items can be used to check the alignment of the annulus and phase ring? ANSWERS B. Multiple Choice Select the answer that best completes the following statements. Multiple Choice 1. A phase-contrast microscope differs from a brightfield microscope by having a a. blue filter in the ocular lens. b, diaphragm with an annular stop. c, phase plate in the objective lens. d. Both (b) and (c) are correct. e. All are correct. 2. If direct rays passing through an object are advanced wavelength by the phase ring, the diffracted rays are a. in phase with the direct rays. b. wavelength of with the direct rays. c. out of phase direct rays. d. in reverse phase with the direct rays. e. Both (b) and (d) are correct.Explanation / Answer
1. In case of bright field microscopy the object can’t be seen without staining. Because bright filed microscopy have low level of contrast and not all the biological samples absorb the light up to great extent. So staining used to increase the contrast, But that technique can’t be used for live cells. In case of phase contrast microscopy the objects observed on the phase shift of light passing through the transparent object. It helps in study of living cells without staining. Staining will cause the cell death if you want to study the live cell.
2. Diffraction is the minimal bending of light as it passes through the outer surface of object. That diffraction of light will depend upon the size of wavelength. When direct light ray. Direct ray comes directly from the source. So direct ray will not affected and phase shift will be zero. In case of diffracted rays it will bend and phase shift of ¼ of the wavelength.
3. Coincidence produces the brighter image and Interference produces the dark images. This will be dark if the destructive interference produced, in which light wave lies over the crest of the other wave.
4. Bright phase will produce the brighter images because of amplitude summation (Direct and diffracted rays are in phase) Dark Phase will produce the darker image because of the amplitude interference (when waves get superposed).
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