(a) A calcite crystal (μₒ = 1.658, μₑ = 1.486) is placed over printed text. Why do you see a double image? (b) In a Nicol prism, Canada balsam has μ = 1.55. Explain which ray is removed and why. Solution: (a) The unpolarized light from the text splits inside the anisotropic calcite into the o-ray and e-ray, which refract by different amounts because μₒ ≠ μₑ. The two plane-polarized images (vibrations at right angles) emerge displaced from each other — hence the double image. Rotating a polarizer over the crystal makes one image disappear at a time, proving each is polarized. (b) The o-ray travels in the denser medium (μₒ = 1.658) toward balsam (1.55): since it goes from higher to lower index at a steep angle exceeding the critical angle, it suffers total internal reflection and is ejected sideways. The e-ray (μₑ = 1.486 < 1.55) enters a denser medium and refracts through normally. Only the plane-polarized e-ray emerges.