# What happens to the index of refraction of a lens if placed in water?

What happens to the index of refraction and focal length of a lens that is initially in air that is then placed in water?

• As Bill Nye used to say, "Try it!". A magnifying glass, a kitchen sink, and sunlight should suffice. Apr 29, 2014 at 12:46

The effect of Snell's law is that the equalivent defraction is set by the ratios of the individual refactravive indexes. So if your lens has a refractive index of 4 in air, and water having $1 \frac 13$, then the effect of putting the lens in water is $4 \div 1\frac 13$ or the same solution as the lense of refractive index $3$ in air.