Question

How will the power of a lens change when its surrounding medium is changed from air to water?

Answer 1

The focal length of the lens will increase as the bending will not be much inside water as it would be in air. Thereby decreasing the power of the lens as P=1/f.
This is because vending occurs as a result of difference in speeds of two media now difference in speed is more in case of air and lens(glass) then in water and lens(glass) and that's why less bending occurs thereby increasing the focal length.