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NBEO Physiological Optics Practice Test

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In terms of Abbe values, which pair of crown glass and CR-39 is known to have relatively high values compared with polycarbonate?
Correct Answer:
They both have relatively high Abbe values compared to polycarbonate
Explanation:
Abbe value reflects how much a material disperses light into colors; a higher Abbe number means less chromatic dispersion and therefore fewer color fringes in a lens. Among common ophthalmic lens materials, polycarbonate has a notably low Abbe value, around the 30s, which means more dispersion. Crown glass and CR-39 both have much higher Abbe numbers (roughly in the upper 50s to around 60), indicating they disperse light less than polycarbonate. Since Abbe value is an intrinsic property of the material, crown glass and CR-39 independently exhibit relatively high Abbe values compared with polycarbonate. The other statements don’t fit because Abbe values aren’t about pairing materials with each other, and polycarbonate does not have the highest Abbe number.

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