Trace Evidence Examination Questions and Answers

Answer: D

The medullary index is diameter of medulla / diameter of hair shaft.

The index compares the width of the central medulla with the width of the whole hair. It is a standard way of telling human from animal hair: in human hair the medullary index is generally less than 1/3, while in most animal hairs the medulla is broad and the index is 1/2 or more.

The other options are inverted or use the wrong measure. Shaft diameter over medulla diameter is the reciprocal of the index, and circumference does not enter the definition, which is a ratio of two diameters.

Answer: D

The common shapes of crystalline pigments are cubic, rectangular and needle-shaped.

Pigment particles are crystals, and the crystal habit decides their shape: blocky cubic or prismatic forms, rectangular plates or blocks, and long needles (acicular forms) are all met in paint and ink pigments. A near-spherical particle is not a crystal habit. An early electron-microscope study (Nature, 1947) found that among commonly used pigments only carbon particles are spherical, and other inorganic pigments give crystalline particles. So (a) does not belong in the list, which leaves (b), (c) and (d).

Options A, B and C each include 'spherical' and so are wrong. This is a textbook-style list; sources classify shapes under slightly different names (prismatic, acicular, lamellar), and we read 'rectangular' with the key.

Answer: C

The setting time of cement is determined with the Vicat apparatus.

The Vicat apparatus has a needle of standard weight that is lowered onto cement paste. The initial setting time is when the needle no longer penetrates to within a set distance of the bottom of the mould; the final setting time is when an annular attachment no longer marks the surface. The same apparatus is used to find the paste's standard consistency.

A Bunsen apparatus is a gas burner, and 'Berner' and 'Burden' apparatus are not cement-testing instruments.

Answer: D

The densest liquid is bromoform.

Approximate densities at room temperature:

• xylene: 0.86 g/cm³
• nitrobenzene: 1.20 g/cm³
• bromobenzene: 1.50 g/cm³
• bromoform (CHBr₃): 2.89 g/cm³

Bromoform's three heavy bromine atoms make it unusually dense, which is why it is used in density-gradient and float-sink methods for comparing glass and soil particles. Xylene is lighter than water, and the other two lie between.

Answer: B

The first hairs formed in the embryo are lanugo hairs.

Lanugo is the fine, soft, unpigmented hair that is the first product of the hair follicles, covering the fetus from about the fifth month. It is usually shed before or shortly after birth.

Vellus hairs are the short, fine hairs that replace lanugo over most of the body after birth, and terminal hairs are the long, coarse, pigmented hairs of the scalp, eyebrows and (after puberty) the body. 'Fuzz hairs' is an informal name, not a developmental stage.

Answer: A

The glass is laminated glass.

Laminated glass is made of layers of glass bonded with plastic interlayers (polyvinyl butyral or polycarbonate). When struck, the glass cracks but the fragments stay attached to the interlayer, and several layers together can stop a bullet. Bullet-resistant screens are built this way, as are car windscreens.

Tempered glass is stronger than ordinary glass but shatters completely into small cubes, so it cannot stop a bullet. Crown glass is an old hand-blown window glass, and 'slit glass' is not a glass type.

Answer: B

The correct match is a-iv, b-iii, c-ii, d-i.

Colouring oxides and compounds give glass characteristic colours: copper in its dissolved, oxidised form produces blue (and blue-green), manganese the familiar purple or violet, nickel shades of yellow to brown, and antimony sulphide a red colour.

The other codes fail on the best-known pairings. Manganese purple is shared by only two options, and of those the one giving antimony sulphide blue is wrong. The remaining two give manganese yellow, which contradicts its use as the classic purple colourant.

Answer: D

Both the assertion and the reason are correct. Hair is a very useful trace, which helps to link suspect and victim with each other and with the scene, since hairs are transferred on contact. That transfer rests on Locard's principle of exchange, that every contact leaves a trace, so the reason explains the assertion.

The other options call one or both statements incorrect, which is wrong: hair does serve this linking role, and Locard's principle is correctly stated.

Answer: B

Lanugo hairs are thin and soft. They are the fine downy hairs that cover a foetus, and they are mostly shed before or soon after birth.

They are not pigmented, since they are fine and light, and they are not medullated, because the medulla is absent or very narrow. Their scale pattern is simple, not complex, so the remaining statements do not describe them. Lanugo is therefore a mark of the foetal stage, and an examiner who finds it on a newborn infant may use it, with other signs, to judge how mature the child was at birth.

Answer: B

Linseed, safflower and cottonseed oils are used as paint oils, that is, vehicles. The drying oils like linseed set by oxidation to make a film.

They are not pigments, which are coloured powders. They are also not solvents, which evaporate, and they are not binders in the sense of the key, which lists them as the paint oils. In paint analysis the oil is the part that dries by oxidation, so identifying linseed, safflower or cottonseed oil by chemical tests helps to date and compare paint evidence, as well as showing what the film is made of.