Rain is falling into a puddle, you notice the distance between each ripple is 0.05m. The waves are spreading out at a rate of about 0.5m/s, what is the frequency of the rain dropping?

In a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. what should be the radius of curvature of the cornea such that the image of an object 40.0 cm from the cornea’s vertex is focused on the retina?