Nature and Perception of Colour Questions and Answers

Answer: D

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 rainbow displays the spectrum, one wavelength at each position, and magenta cannot be produced by any single wavelength - it requires long and short wavelengths together with the middle absent. Magenta is therefore non-spectral, and so are the purples generally, which is why the chromaticity diagram is closed by a straight line rather than a curve.

Answer: A

Correct answer: False

The spectral colours are only the boundary of what can be seen. The purples and magentas are non-spectral, requiring red and blue together; and every unsaturated colour - pink, brown, olive, grey - is a mixture with no single wavelength of its own. Brown in particular corresponds to no spectral line at all, being a dark orange judged against a brighter surround.

Answer: B

Colour arises from several quite different physical mechanisms. Structural colours from interference and diffraction shift with the viewing angle in a way absorption colours do not. Geometry governs one and chemistry the other.

Answer: C

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. Structural colour arises from interference and diffraction in physical structures of a size comparable to the wavelength, and both effects depend on the path difference and hence on the angle. Absorption colour depends on which wavelengths the molecules take up, which does not change with the direction of view - hence the iridescence of a beetle against the steadiness of a dyed cloth.

Answer: D

Correct answer: scattering that is stronger at short wavelengths

Rayleigh scattering by molecules much smaller than the wavelength varies as the inverse fourth power of wavelength, so blue light is scattered some ten times as strongly as red. The scattered light reaching the eye from all directions is therefore blue, and the direct beam, depleted of blue, reddens as its path through the atmosphere lengthens at sunset.

Answer: A

Both are true and the reason gives the mechanism, and only the longer wavelengths survive the journey. One phenomenon is the complement of the other. Path length through the atmosphere decides which. Low sun means a long path and a red result.

Answer: B

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

Four attributes describing four different things. Hue is the attribute named by the colour words. Lightness is brightness judged relative to a similarly lit white, which is what makes it independent of the light level. Chroma is colourfulness judged against the same white reference, and saturation is colourfulness judged against the stimulus’s own brightness - the same quantity referred to two different denominators.

Answer: C

Correct answer: judged relative to a similarly illuminated white reference

Brightness is an absolute judgement of how much light appears to come from a surface; lightness is that judgement made relative to a white in the same illumination. The relative form is the useful one, because it stays roughly constant as the light level changes - which is why a sheet of paper is white indoors and out.

Answer: D

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

Both are true and the reason explains why. In dim light the paper sends far less light to the eye, so its brightness falls, but everything around it falls in the same proportion; lightness, being the ratio, is unchanged. The visual system judges surfaces against their surround rather than absolutely, and that is what makes surface colours stable across a wide range of illumination.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 give the two definitions correctly. Statement 3 collapses a distinction that matters: chroma is referred to a similarly lit white and saturation to the stimulus’s own brightness, so a colour in shadow keeps its saturation while its chroma falls. Confusing the two makes appearance predictions go wrong wherever the illumination is uneven.