Spectrophotometry and Colorimetry Questions and Answers

Answer: C

Correct answer: remove the specular component from the measurement

The gloss trap is an opening in the sphere wall placed where the specular reflection from the sample falls, backed by a light-absorbing cavity. With it open the specular light is absorbed and the measurement is specular excluded; with it closed and made part of the sphere wall, the light is retained and the measurement is specular included.

Answer: D

Correct answer: high and uniform diffuse reflectance across the spectrum

The sphere works by multiple diffuse reflections, so the coating must scatter rather than mirror, must reflect nearly all the light so that little is lost in the many bounces, and must do so equally at every wavelength. Any spectral structure in the coating would be multiplied by all those reflections and would colour every reading.

Answer: A

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. Light bounces many times inside the sphere before reaching the detector, so any wavelength dependence of the coating is applied repeatedly and amplified. A coating that reflected slightly less in the blue would make every sample read slightly yellow, and no calibration on a white tile would fully remove it.

Answer: B

Any change in the coating alters the flux reaching the detector. Regular verification against a reference tile detects such drift early. Flux reaching the detector changes with the coating. Verification tiles reveal the change.

Answer: C

Its reflectance values are certified against a perfect reflecting diffuser. The tile itself must be kept clean and recalibrated periodically. Values are certified against a perfect diffuser. Traceability runs back to a national standard.

Answer: D

Both are true and the reason gives the reason, and an uncorrected drift propagates into every measurement. A working tile and a reference tile are often kept separately. Handling and cleaning both alter the reflectance.

Answer: A

It has a reflectance of one at every wavelength and scatters perfectly. Real tiles are calibrated against it rather than being it themselves. It is a theoretical construct rather than an object. Real tiles approximate it to a stated uncertainty.

Answer: B

Correct answer: check the zero reflectance response and the stray light

The black trap presents as near to zero reflectance as can be made, so whatever the instrument then reports is the sum of its electronic zero error and any stray light reaching the detector by an unintended path. Together with the white tile, it fixes the two ends of the reflectance scale.

Answer: C

Both are true and the reason gives the logic, and dark samples are the most affected. A trap measurement is part of routine verification. Dark samples are where it matters most. The lightness function amplifies the error further.

Answer: D

The first two are correct and are the two basic checks. The third is wrong, since verification is a routine daily or weekly activity. Drift accumulates without any obvious symptom. Routine checking is the only defence.