Skip to main content
Engineering LibreTexts

10.8: Questions

  • Page ID
    36282
  • Deeper questions

    The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

    How should the initial focusing of the microscope be done?

    a With the coarse focus moving the lens towards the specimen.
    b With the fine focus moving the lens towards the specimen.
    c With the coarse focus moving the lens away from the specimen.
    d With the fine focus moving the lens away from the specimen.
    Answer

    C

    the fine focus tends to have a limited range and so not only would it take a long time to bring the specimen into focus, but it may not go far enough to bring the specimen into focus.

    The specimen preparation is important in metallurgy because:

    a A poorly prepared specimen can damage the microscope.
    b A poorly prepared specimen will distract from features on the specimen.
    c Only a well prepared specimen will reflect light.
    d A poorly prepared specimen will corrode, and the resulting images will be misleading.
    Answer

    B

    unless the microscope is misused, a specimen will not damage the microscope.

    the preparation does not cause the specimen to reflect light, but allows features to be picked out.

    a poorly prepared specimen will not corrode any faster than a properly prepared specimen.

    When increasing the magnification on the microscope, which of the following occurs?

    a The depth of field increases.
    b The resolution limit decreases.
    c The visible area decreases.
    d The contrast increases.
    Answer

    C

    the depth of field decreases as the magnification increases.

    the resolution limit stays the same.

    the contrast is not affected by the magnification .

    When the aperture stop is made smaller, which of the following occur?

    Yes No a The depth of field increases.
    Yes No b The resolution decreases.
    Yes No c The contrast increases.
    Yes No d The brightness increases.
    Answer

    A Yes

    B Yes

    C Yes The contrast may increase slightly, but if the aperture stop is closed too far, diffraction fringes may be produced, giving rise to misleading pictures.

    D No The brightness is reduced as the aperture stop is made smaller as this restricts the amount of light reaching the specimen.

    The red tint plate (also known as a full wave sensitive tint plate) increases the contrast in a polarised light microscope because:

    a Our eyes are more sensitive to red light, so it is easier to see the light and dark areas when there is a red tint plate.
    b The red tint plate only lets a small window of wavelengths through, and so increases the birefringence.
    c The red tint plate displaces the ordinary and the extraordinary beams by an extra wavelength, so that small differences in birefringence cause large differences in colour.
    d The red tint plate increases the differences in birefringence in the material so that the different grain directions cause a greater difference in colour than in just the polarised light.
    Answer

    C

    human eyes are most sensitive to the green region of light.

    the red tint plate lets through all visible wavelengths of light.

    the tint plate does not affect the birefringence of the material.

    Contrast in reflected microscopy tends to be caused by:

    a Variations in topography and differences in reflectivity of areas.
    b Only differences in reflectivity of areas.
    c Only topography.
    d Variations in thickness of the specimen.
    Answer

    A

    it can also be caused by topography.

    it can also be caused by differences in reflectivity of areas.

    contrast is caused by variations in topography and differences in reflectivity of areas.

    If a graticule is observed under the 10x lens of a microscope so that the diameter of the field of view is from 150 μm to 450 μm on the graticule, what is the width of one lamella when it takes 15 lamellae to fill the field of view when viewed under the 50x lens.

    Answer

    The field of view under the 10x lens is 450 μm - 150 μm = 300 μm.

    So the field of view under the 50x lens is 300 μm/5 = 60 μm.

    If 15 lamellae fill the field of view, then each lamella must be 60 μm/15 = 4 μm across.

    • Was this article helpful?