For light at a wavelength of 1 = 656.3 nm water (at 20 C) has an

For light at a wavelength of λ₁ = 656.3 nm water (at 20° C) has an index of n₁ = 1.3311. At a wavelength of λ₂ = 89.3 nm water has an index of n₂ = 1.333 0. Determine the approximate value of the group velocity of light in water. Is v̅ > v_g? [Hint: Reread Problem 7.36, approximate the differentials by finite differences, and remember the little ω̅ in the definition of v_g. Be careful of the slope of n versus λ.]