Practice question

**Refraction at plane surface** changes direction due to speed change v = c/n, n = c/v. For water n=1.33 to air, n₁>n₂, ray bends away, if θ₁ > C, sinθ₂>1 impossible, TIR occurs. Snell's law quantitative prediction of θ₂ from θ₁ and indices. Focal length: f = -6 cm (concave mirror). Object distance: u = -12 cm . Mirror equation: (1/v) + (1/u) = (1/f) . (1/v) + (1/-12) = (1/-6) ⇒ (1/v) = (1/-6) + (1/12) = (-2 + 1/12) = (-1/12) . v = -12 cm (real image). Substituting values gives 12 cm, which matches expected image position and magnification from mirror/lens formula