The daily average insolation on the earth surface is approximately 6 kWh/m2 (ignoring cloudy weather). If a commercially available solar panel can achieve an energy conversion efficiency of 20%, what is the area that is required to supply the electricity demand of the US in 2014 (the population was about 324 million and the average per capita power was 1378 watts). What is the fraction (or multitude) of Tennessee (109,250 km2) that is required to power the entire US.

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.)