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Questions and Answers
What is the primary purpose of the scanning objective lens in a microscope?
What is the primary purpose of the scanning objective lens in a microscope?
- To enable observation of specimens using immersion oil.
- To offer the lowest magnification for a general overview of the slide. (correct)
- To facilitate the highest power magnification of specimens.
- To provide a detailed view of fine specimen details.
Which equation is correctly used to determine the actual size of an object from its magnification?
Which equation is correctly used to determine the actual size of an object from its magnification?
- Actual Size = Image Size + Magnification
- Actual Size = Image Size × Magnification
- Actual Size = Image Size ÷ Magnification (correct)
- Actual Size = Magnification ÷ Image Size
What is required for the oil immersion objective lens to function correctly?
What is required for the oil immersion objective lens to function correctly?
- A clean glass slide without any oil.
- Only air between the lens and the specimen.
- A drop of immersion oil to bridge the refractive index gap. (correct)
- A higher voltage source for better clarity.
When combining a 40X objective lens with a 10X ocular lens, what is the total magnification?
When combining a 40X objective lens with a 10X ocular lens, what is the total magnification?
What distinguishes the high power objective lens from the low power objective lens?
What distinguishes the high power objective lens from the low power objective lens?
What is a significant limitation of using a two lens system for magnification?
What is a significant limitation of using a two lens system for magnification?
What characteristic of dark field microscopy allows unstained samples to appear brightly lit?
What characteristic of dark field microscopy allows unstained samples to appear brightly lit?
Which of the following specimens is best suited for observation under dark field illumination?
Which of the following specimens is best suited for observation under dark field illumination?
How does dark field microscopy improve visualization of a specimen compared to bright field microscopy?
How does dark field microscopy improve visualization of a specimen compared to bright field microscopy?
What visual effect is often observed when examining pigmented objects under dark field microscopy?
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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