Spectrophotometry and Colorimetry Questions and Answers

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: inter-instrument agreement sets the limit on how usefully data can be exchanged, and profiling to a master improves it. Statement 3 is the misconception the whole subject exists to correct - two instruments of the same model differ, by amounts that matter against commercial tolerances, and the differences must be measured and corrected rather than assumed away.

Answer: D

The amount of ultraviolet determines how much the brightener fluoresces. An adjustable filter is set so the source matches the reference illuminant. Brightener response depends directly upon it. The setting must match the reference illuminant.

Answer: A

Correct answer: A-2, B-4, C-1, D-3

Four ultraviolet conditions. With ultraviolet included the full source output reaches the sample, so any brightener fluoresces fully. With it excluded a filter removes the ultraviolet entirely and the brightener contributes nothing. UV calibrated sets the ultraviolet content to match a defined illuminant, and the adjustable filter is the mechanism by which that setting is made.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. A fluorescent brightener works by absorbing ultraviolet and re-emitting it in the blue, adding light the illuminant never supplied. Remove the ultraviolet and there is nothing to convert, so the sample reads as the substrate alone - markedly less white than it appears in daylight.

Answer: C

Only a fluorescent standard responds to the ultraviolet setting at all. A non-fluorescent tile would give the same reading whatever the filter position. Only fluorescence responds to the setting. A plain tile reads the same throughout.

Answer: D

It gives the same reading regardless of the ultraviolet content. Only a fluorescent standard responds to the setting being adjusted. A plain white tile is useless for the purpose. A fluorescent standard is required instead.

Answer: A

Correct answer: the area measured, the backing and the number of layers

All three change what the instrument sees. The area determines how much of a non-uniform surface is averaged; the backing matters wherever light passes through the sample and returns; and the number of layers determines whether it is opaque at all. Each must be recorded with the measurement if it is to be reproduced.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the cause. A translucent sample transmits part of the light, which reaches the backing, is reflected from it and returns through the sample to the detector. The reading therefore depends on what the backing is - white, black or another layer of the sample - and is not reproducible unless the backing is stated.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: a translucent sample needs a specified backing, and folding fabric to enough layers makes it effectively opaque. Statement 3 contradicts both, and it is wrong by a wide margin - presentation is often the largest source of disagreement between two laboratories measuring the same material.

Answer: D

A textured or printed sample requires a large enough aperture to average properly. Small apertures are used where only a small uniform area is available. Texture needs a large aperture to average. Small apertures suit small uniform areas.