Spectrophotometry and Colorimetry Questions and Answers

Answer: A

Both are true and the reason gives the comparison, and averaging addresses the larger source of error. Chasing instrument precision beyond that point yields little benefit. Averaging addresses the larger source of error.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: sample non-uniformity is very often the largest contribution, and averaging over positions reduces it. Statement 3 is the misconception - instrument repeatability is usually the smallest term of the three, and an uncertainty estimate based on it alone will be far too optimistic.

Answer: C

Departures from the exact functions introduce systematic errors for some samples. Metameric samples in particular are handled poorly. Filter departures introduce systematic errors. Metameric samples expose them most clearly.

Answer: D

Both are true and the reason gives the limitation, and the error depends on the sample spectrum. Spectral instruments avoid the problem entirely. The filters only approximate the true functions. Exact agreement would require the Luther condition.

Answer: A

Correct answer: be a linear combination of the colour matching functions

The Luther condition is what makes an instrument a true colorimeter: if its spectral responsivities are linear combinations of the colour matching functions, it will match whatever the standard observer matches, including metameric pairs. Real filter colorimeters approximate it imperfectly, which is why they disagree with a spectrophotometer on metamers.

Answer: B

Drift accumulates gradually and is not announced by any obvious symptom. A verification record provides evidence that past measurements were sound. Drift is silent and gradual. Records support later investigation of a dispute.

Answer: C

Both are true and the reason gives the additional value, and a dispute may turn on it. Records are normally retained for the life of the product. A dispute may turn on the record. Retention periods are set accordingly.

Answer: D

Correct answer: 2 - 4 - 1 - 3

Warm up first, since the source and the electronics drift until they are stable and a calibration made cold will not hold. Then calibrate on the white and black standards, which sets the scale. Then measure the verification tiles, which are independent of the calibration and so test it. Finally record the result and either proceed or investigate.

Answer: A

Correct answer: sets the instrument scale using known standards

Calibration adjusts the instrument so that it reads correctly on standards of known value; verification measures independent standards afterwards to see whether it does. The distinction matters because an instrument that has been calibrated has not thereby been shown to be right - only the verification, on standards not used in the calibration, shows that.

Answer: B

Both are true and the reason gives the logic, and the check would pass regardless. Independent verification is the whole point of the exercise. The check would otherwise pass regardless. Independence is the entire point.