By coating iron with oil protect it from being exposed to atmoshphere. The atmoshpher contains oxygen which is responsible for corrosion. Oxidation reaction takes place when iron surface reacts with oxygen which cause rusting of iron.
In both the common problem is continuity. Wind flow is a variable factor also same for the water flow.
So the power generation would be discontinuous and discrete. Aslo there is problem with a constant frequency power which is required by the electrical equipments to work. But this issue can be solved using power electronics circuit.
When light travels from denser to rarer medium, the angle of incidence at which angle of refraction is 90 degree is called critical angle of incidence and increasing beyond that critaical value then light gets reflected to same medium.
When scientists talk about the expanding universe, they mean that it has been growing ever since its beginning with the Big Bang. The galaxies outside of our own are moving away from us, and the ones that are farthest away are moving the fastest.