Lenses - Why do light rays bend less in water?

[Padfoot]

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I understand that the difference in refractive indexes is less with lenses in water compared to air, but I'm having trouble understanding why the light rays will bend less mathematically. Do I use snell's law?

Also, why does less bending mean a less powerful lens? Does that mean the refractive index of the lens is lower, so the light rays don't bend toward normal as much?

 

[Cawolf]

The lensmakers equation says that 1/f = P = (nlens-nmedium)/nmedium * (1/R1 + 1/R2)

Assuming the radius of the lens is constant, then the power will decrease as the difference in refractive index between the lens and medium decreases.

Snell's Law will show how the angle of refraction depends on the refractive index of the material - so it could be applied to see how n effects the bending of the light.