Transparent plastic swimming-pool covers called solar heat sheets have thousands of small air-filled bubbles that resemble lenses. The bubbles in these sheets are advertised to focus heat from the sun into the water, thereby raising its temperature. Do you think these bublles direct more solar energy into the water? Defend your answer.
No, because the air in the bubbles has the same refractive index as the air outside.
No these can not because the total area of the lenses is not grater then the pool the total sunlight that falls on the pool remains same, or even less because some light is absorbed in sheet. but sheet can help in heating the water because it do not allow water to loose heat due to evaporation It acts as like a greenhouse shield
The best cover would be as the one described but with a black underside which would absorb the sunlight converting it to hat which would be transferred to the water. The air bubbles do 2 things, They make the cover float and they act as a heat insulating layer preventing the heat of the water escaping. Their efficacy as a lens is doubtful.
