Spectrophotometry and Colorimetry Questions and Answers

Answer: A

Correct answer: the medium term stability of the instrument

Repeating the same measurement on the same instrument after an interval isolates drift: the sample and the method are unchanged, so any difference is the instrument moving over that period. Repeatability is measured over minutes and reproducibility between instruments; this is the term between them, and it governs how often recalibration is needed.

Answer: B

Both are true and the reason gives the purpose, and the control must itself be stable. Ceramic tiles are preferred over textile samples for this role. A drifting control cannot detect drift. Stability is the first requirement.

Answer: C

A drifting control cannot distinguish its own change from the instrument's. Stability is the primary requirement for anything used as a reference. Uniformity and cleanability matter too. Ceramic tiles satisfy all three requirements.

Answer: D

Correct answer: strong fluorescence under ultraviolet

A control sample is measured repeatedly to detect instrument drift, so its own colour must be as stable and as reproducible as possible. Fluorescence makes the reading depend on the ultraviolet content of the source, which is itself liable to drift - so a fluorescent control would confound the very thing it is meant to detect.

Answer: A

Correct answer: any later recalculation for a different illuminant

Tristimulus values are computed from the spectrum for one particular illuminant and observer, and the spectrum cannot be recovered from them. Store only the values and the data can never be recalculated for another illuminant, so metamerism cannot be assessed and a change of standard illuminant means measuring everything again.

Answer: B

Correct answer: the ambient noise level in the laboratory

Sound has no effect on a colour measurement. The other three all change the result and must be recorded if it is to be reproduced: the layers and backing determine what light returns through a translucent sample, the geometry and specular condition determine what the instrument collects, and the ultraviolet setting determines whether a brightener contributes.

Answer: C

These conditions change the physical measurement rather than merely its interpretation. Agreeing them in advance removes most of the disagreement. These conditions change the physical measurement. Agreement in advance prevents the dispute.