UGC NTA NET/JRF Exam, Forensic Science, January-2025

A spectrophotometer is an analytical instrument designed to measure how much light a sample absorbs at a given wavelength. Its components are always arranged in a fixed optical sequence so that radiation travels step by step through them. Let's examine each:

B. Radiation source: This is the starting point. Depending on the type of spectrophotometer, it could be a tungsten lamp (visible), deuterium lamp (UV), or Globar/Nernst lamp (IR). It provides the continuous spectrum of light needed.

D. Monochromator: The light from the source is polychromatic. A monochromator (prism or diffraction grating) selects and isolates a narrow band of wavelengths so only specific light reaches the sample.

A. Sample holder: Here, the light passes through the sample solution (in a cuvette). The sample absorbs part of the radiation according to its molecular properties.

E. Detector: After leaving the sample, the remaining transmitted light strikes the detector. The detector (photocell, photomultiplier tube, or photodiode array) converts light into an electrical signal proportional to intensity.

C. Recorder: The signal is amplified and displayed digitally or as a spectrum curve, giving the absorbance/transmittance values.

Thus, the sequence is: Radiation Source → Monochromator → Sample Holder → Detector → Recorder.

Rationale (by evidentiary value → strongest to weaker among the given choices):

A. Fingerprint: When ridge detail is sufficient, latent prints provide direct individualization (one-to-one identification). Courts treat a high-quality fingerprint match as very high probative value.

B. Blood spots: Typically yield nuclear DNA STR profiles with extremely high discrimination power and may also support bloodstain pattern analysis. Among biologicals, blood generally gives the most robust DNA recovery.

D. Saliva: Also a DNA source (buccal epithelial cells), highly probative but often lower DNA yield/quality than blood; still strong but typically ranked just below blood.

C. Bite mark: The pattern evidence aspect is controversial and now considered limited probative value; it should be photographed and documented early, but its intrinsic evidentiary weight is below DNA/prints.

E. Fallen hair: Frequently telogen (no root) → often only mtDNA (maternal lineage) or morphology, so lower individualizing power unless a root is present.

Among the provided sequences, Option 1 is the best fit for ordering by evidentiary value while keeping lower-value items (bite mark, shed hair) after high-value identifiers (prints/DNA).

On many bullets, you see grooves or knurled impressions cut around their circumference. These are called cannelures. Their functions include:

Securing the bullet in the cartridge case: The case mouth is crimped into the cannelure to prevent the bullet from being pushed backward during feeding or moving forward under recoil.

Lubricant or sealing groove: Some cannelures are designed to hold lubricant or sealant to improve performance.

Identification feature: The presence, number, and type of cannelures can help a forensic examiner narrow down the possible manufacturer or type of ammunition.

Cannelures must be distinguished from rifling marks (lands and grooves) - the former are manufactured features on the bullet, while rifling marks are microscopic striations imparted by the firearm's barrel.

In rifled firearms, the term calibre is used to describe the bore diameter (e.g., 0.22 inch, 7.62 mm). However, in shotguns, the bore size is expressed differently - it is called the gauge.

• The gauge is defined as the number of spherical lead balls of bore diameter that together weigh one pound.

• For example, in a 12-gauge shotgun, 12 lead balls of the bore's diameter equal one pound. Similarly, in a 20-gauge, 20 such balls equal one pound.

• A smaller number means a larger bore diameter (so a 12-gauge bore is wider than a 20-gauge bore).

This system is unique to shotguns and is important in forensic firearm examination when estimating weapon type from fired pellets or wads.

In firearms investigation, examiners look for information that helps establish the weapon used, the shooter's actions, and the link between suspect and firearm:

Type of firearm used: Identifying whether it was a revolver, pistol, rifle, or shotgun is fundamental to an investigation.

Direction of bullet travel on glass: Determines shooter's position (entry vs. exit side of glass).

Linkage of the shooter to the firearm: Achieved by comparing bullets, cartridge cases, fingerprints, or DNA; it directly associates a suspect with the weapon.

Terminal velocity of the bullet at the target point: Although it has scientific value, it usually does not assist the investigation.

Exact velocity at impact rarely helps in determining the shooter, firearm type, or reconstruction, since wound ballistics focuses more on entry/exit, range, and direction than on speed at target.

Rifling can be produced by several methods (broaching, swaging, hammer forging, electrochemical etching). Among them, broaching - which uses a toothed cutting tool pulled through the barrel - tends to leave sharper, well-defined microscopic striations on the bore surface.

These striations get transferred onto fired bullets, producing markings that are more useful for forensic comparison than the smoother marks produced by swaging, hammer forging, or etching.

The most common industrial blasting explosive is Ammonium Nitrate mixed with fuel oil (ANFO). This mixture is inexpensive, safe to handle, and powerful enough for mining and construction. Neither nitroglycerin, nitrocellulose, nor dynamite are mixed in this way for large-scale blasting; ANFO is the correct choice.

When Alfred Nobel invented dynamite, he stabilized nitroglycerine by absorbing it in an inert, porous material called kieselguhr (a diatomaceous earth).

This made handling nitroglycerine far safer, reducing the risk of accidental explosions during transport and use. This mixture was called "Ghur Dynamite".

Storage media are devices where data can be stored long-term, such as HDD (Hard Disk Drive), SSD (Solid State Drive), and Pen Drive. CPU (Central Processing Unit), however, is not a storage medium; it processes instructions and executes tasks.

Fingerprints are unique to an individual, whereas questioned documents and tool marks are often unique but not always definite.

Fingerprints: The ridge patterns and minutiaе on fingers are unique and permanent. Even identical twins have different prints.

When clear and complete impressions are obtained, they allow for conclusive and individual identification. This makes fingerprints one of the strongest forms of forensic evidence.

Questioned Documents: These involve analysis of handwriting, signatures, typewriting, and printing. While handwriting often contains individualizing features, it can vary due to disguise, health, or stress.

Forgeries can be close imitations. Hence, document examination provides strong evidence but not always to the same absolute certainty as fingerprints.

Tool Marks: These are impressions left by tools on softer surfaces. They show class characteristics (shared by all similar tools) and individual characteristics (unique wear/ defects).

However, the appearance of a tool mark can vary with angle, pressure, and surface, meaning conclusions can be highly indicative but not always definitive.

Thus, the key difference is that fingerprints provide individual uniqueness, while questioned documents and tool marks, though often highly suggestive, are not guaranteed to be infallibly conclusive.