Forensic Microscopy
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1
What is forensic microscopy?
The use of microscopes to examine and compare evidence features too small to assess adequately with unaided vision.
2
What is magnification in microscopy?
The ratio of an image's apparent size to the actual size of the observed object.
3
What is resolving power in microscopy?
The ability of an optical system to distinguish two closely spaced features as separate.
4
Why is resolution more important than magnification alone?
Enlarging an image does not reveal additional detail when the instrument cannot resolve that detail.
5
What is a compound light microscope?
A microscope using an objective lens and an eyepiece or imaging system to magnify specimens with visible light.
6
How is total magnification calculated in a conventional compound microscope?
Multiply the objective magnification by the eyepiece magnification.
7
What is the total magnification of a 10× eyepiece with a 40× objective?
400×.
8
What is the function of a microscope objective lens?
To collect light from a specimen and form the primary magnified image.
9
What is numerical aperture in microscopy?
A measure of an objective's ability to gather light and resolve fine specimen detail.
10
What is the relationship between numerical aperture and optical resolution?
Higher numerical aperture generally permits better resolution when other relevant conditions are comparable.
11
What is a stereomicroscope?
A low-to-moderate magnification microscope that provides a three-dimensional impression useful for examining object surfaces.
12
Why is stereomicroscopy useful for trace evidence?
It permits examination, sorting, and manipulation of small particles or fibers with relatively large working distance.
13
What is working distance in microscopy?
The distance between the objective lens and the specimen when the image is in focus.
14
What is a comparison microscope?
An instrument that permits simultaneous viewing of two specimens through linked optical systems.
15
What is the forensic purpose of a comparison microscope?
To assess similarities and differences between questioned and known specimens under comparable viewing conditions.
16
Does observing similar features through a comparison microscope automatically establish a common source?
No. The significance depends on the features, examination method, and relevant limitations.
17
What is bright-field microscopy?
An optical method in which the specimen is viewed against a relatively bright background using transmitted illumination.
18
What is dark-field microscopy?
A technique in which scattered light from a specimen produces a bright image against a dark background.
19
What is phase-contrast microscopy?
A method that converts phase differences in light passing through a specimen into visible contrast.
20
What is polarized light microscopy or PLM?
Microscopy using polarized light to examine optical properties of materials such as fibers, minerals, and crystalline particles.
21
What is birefringence?
The optical property of certain materials in which light experiences different refractive indices depending on its polarization or direction.
22
What is extinction in polarized light microscopy?
A condition in which an anisotropic specimen appears dark at particular orientations between crossed polarizers.
23
What is the significance of refractive index in microscopic material examination?
It helps characterize and compare transparent materials through their interaction with light.
24
What is immersion microscopy?
The examination of a specimen placed in a liquid of known refractive index to evaluate its optical properties.
25
What is the Becke line?
A bright line near the boundary of materials with different refractive indices, used in certain optical comparisons.
26
What is fluorescence microscopy?
Microscopy that detects light emitted by a specimen after excitation with appropriate illumination.
27
What is a scanning electron microscope or SEM?
An instrument that scans a specimen with an electron beam to produce detailed information about surface features.
28
What is a transmission electron microscope or TEM?
An instrument that forms images using electrons transmitted through a sufficiently thin specimen.
29
What is a major distinction between SEM and TEM?
SEM commonly examines surface morphology, while TEM examines internal structures in thin specimens.
30
What is energy-dispersive X-ray spectroscopy or EDS?
An analytical technique that detects characteristic X-rays to provide information about elemental composition.
31
Why is SEM-EDS useful in forensic material analysis?
It combines detailed microscopic examination with elemental characterization of suitable particles.
32
What is spectroscopy?
The study or measurement of interactions between electromagnetic radiation and matter.
33
What is infrared spectroscopy?
An analytical technique measuring infrared interactions with molecules to obtain information about chemical structure or composition.
34
What does FTIR stand for?
Fourier-transform infrared spectroscopy.
35
What is the fingerprint region of an infrared spectrum?
A complex spectral region containing absorption patterns that may help distinguish chemical substances.
36
What is Raman spectroscopy?
A technique that examines inelastic scattering of light to obtain information about molecular vibrations.
37
What is ultraviolet-visible spectroscopy or UV-Vis?
A method measuring absorption or transmission of ultraviolet and visible light by a sample.
38
What is atomic absorption spectroscopy or AAS?
An analytical method measuring light absorbed by free atoms to determine concentrations of selected elements.
39
What is X-ray fluorescence or XRF analysis?
A technique using characteristic emitted X-rays to identify or quantify elements in suitable materials.
40
What is chromatography?
A separation technique in which components distribute differently between a stationary phase and a mobile phase.
41
What is the stationary phase in chromatography?
The material or phase that remains in place and interacts differently with components of a mixture.
42
What is the mobile phase in chromatography?
The fluid that moves through or across the stationary phase and transports sample components.
43
What is thin-layer chromatography or TLC?
A separation method using a thin stationary layer on a support and a moving solvent.
44
What is retention factor or Rf in thin-layer chromatography?
The distance traveled by a substance divided by the distance traveled by the solvent front under the same conditions.
45
A TLC spot moves 3 cm while the solvent front moves 6 cm. What is its Rf?
0.50.
46
What is gas chromatography or GC?
A technique that separates suitably volatile compounds using a gaseous mobile phase and a chromatographic column.
47
What is high-performance liquid chromatography or HPLC?
A technique that separates mixture components using a liquid mobile phase driven through a chromatographic system.
48
What is mass spectrometry?
An analytical technique that measures mass-to-charge ratios of ions to help identify or characterize substances.
49
What is the purpose of coupling chromatography with mass spectrometry?
Chromatography separates mixture components while mass spectrometry supplies additional information for identification or characterization.
50
Scenario: Two fibers appear identical under a stereomicroscope but produce different infrared spectra. What is the appropriate interpretation?
Their visible similarity does not establish chemical equivalence; the spectral differences may support distinguishing the fibers.
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