The gravitational potential energy is LEAST when you are on the shore of the dead sea because if you are on top of mount Everest, on the roof of your dwelling, and even at sea level, your gravitational potential energy is GREATER than being on the shore of the dead sea.
Because the closer you are to the center of the earth, the more powerful the earth's gravity is. The top of Mt. Everest is much farther away from the center of the earth than any of the other places.
It would cause the lens to produce only real images. It would cause the lens to produce only virtual images. It would make the lens stronger. It would make the lens weaker.
