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Questions and Answers
What is the primary purpose of the scanning objective lens in a microscope?
Which equation is correctly used to determine the actual size of an object from its magnification?
What is required for the oil immersion objective lens to function correctly?
When combining a 40X objective lens with a 10X ocular lens, what is the total magnification?
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What distinguishes the high power objective lens from the low power objective lens?
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What is a significant limitation of using a two lens system for magnification?
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What characteristic of dark field microscopy allows unstained samples to appear brightly lit?
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Which of the following specimens is best suited for observation under dark field illumination?
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How does dark field microscopy improve visualization of a specimen compared to bright field microscopy?
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What visual effect is often observed when examining pigmented objects under dark field microscopy?
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Study Notes
Microscope Fundamentals
- Smallest distinguishable distance between two points is measured in micrometers (μm).
- Contrast enables detection of different specimen regions based on intensity or color.
Magnification
- Apparent size increase achieved by convex lenses; a compound microscope uses two lens sets for magnification.
- Total magnification formula: Total Magnification = Objective Magnification x Eyepiece Magnification.
- Example: Objective Mag = 40X, Eyepiece Mag = 10X, resulting in Total Mag = 400X.
Objective Lenses
- Scanning Objective Lens (4x): Lowest magnification; provides a general overview of the slide.
- Low Power Objective (10x): Greater magnification; ideal for observing slide samples without excessive detail.
- High Power Objective Lens (40x): Known as “high dry” lens; best for fine detail analysis of specimen samples.
- Oil Immersion Objective Lens (100x): Highest magnification; requires immersion oil to improve clarity due to refractive index differences.
Magnification Calculations
- Magnification can be calculated if either image size or actual size is known.
- Formulas include:
- Magnification = Image Size ÷ Actual Size
- Actual Size = Image Size ÷ Magnification
- Image Size = Actual Size × Magnification
Microscopy Techniques
- Dark Field Microscopy: Illuminates unstained samples against a dark background for enhanced visibility; uses opaque disc to scatter only reflected light.
- Effective for viewing small aquatic organisms, diatoms, unstained bacteria, and protozoa.
Differential Interference Contrast (DIC)
- Generates a 3D image using polarized light split into two beams.
- Beams interact with specimen thickness, leading to brightness variations showing refractive index differences.
Fluorescence Microscopy
- Utilizes fluorescence and phosphorescence for imaging; allows observation of substances that absorb and emit light differently.
- Light sources include xenon arc lamps, mercury-vapor lamps, lasers, and high-power LEDs.
- Employs dichroic mirrors and filters to isolate specific wavelengths of emitted light.
Digital Holographic Microscopy (DHM)
- Utilizes interference patterns generated by overlapping laser beams to create a hologram of the sample.
- Advantages include static and dynamic 3D imaging, auto digital focus for quick scanning, and non-invasive techniques for live cells.
Scanning Tunneling Microscopy (STM)
- Based on tunneling electrons between a conductive probe and a conductive sample surface.
- The probe is moved closely to the sample; the resulting tunneling current provides detailed surface images.
Tunneling Phenomenon
- Describes how electrons move across gaps between objects with different electric potentials when in close proximity.
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Description
Test your knowledge on key microscopy concepts including resolution, contrast, and magnification. This quiz covers important terms and calculations for understanding the functioning of a compound microscope.