A coaxial cable consists of an inner cylindrical conductor of radius 3 cm on the axis of an outer hollow cylindrical conductor of inner radius 7 cm and outer radius of 10 cm. The inner conductor carries current 4.5 A in one direction, and the outer conductor carries current 8 A in the opposite direction. (a) What is the value of the magnetic field at distances 8 cm and 20 cm from the axis of the cable? (b) Draw how the magnitude of the magnetic field changes with the distance from the axis of the cable.

People with normal vision cannot focus their eyes underwater if they aren't wearing a face mask or goggles and there is water in contact with their eyes. 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. with the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 2.05cm in front of the eye.)