When running at its operating speed, a 215-V dc motor with an armature whose resistance is 1.20 Ω draws a current of 25.0 A. What is the back emf of the motor when it is operating normally?

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?