An optician is selecting a front-surface material for thin spectacle lenses that will ultimately interface with the tear film of the eye (index ntear=1.336). Two candidate plastics are being considered:
• Polycarbonate: n=1.586
• CR-39: n=1.498
During typical use, light from an object in air meets the lens surface at an angle of 25∘ to the normal. For each material, the front surface is air-to-plastic and the back surface is plastic-to-tear film; the surfaces are taken to be parallel for this analysis.
(a) For polycarbonate, calculate the angle the light makes with the normal inside the plastic immediately after entering from air.
(b) Still for polycarbonate, determine the angle of the ray in the tear film after it exits the back surface of the lens.
(c) Repeat parts (a) and (b) for CR-39 plastic.
(d) Using your results, decide which material yields the smaller overall deviation of the ray from its original path in air. Justify your recommendation quantitatively and discuss one practical implication for image quality in the wearer’s vision.