Please help! What's the answer to this question? A 5.6 nC electric charge is placed in an Electric Field and experiences a force of 7.4 μN. What is the magnitude of the Electric Field at that location?

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 1.90