What happens to be focal length of convex lens when it is immersed in water?

What happens to focal length of a concave mirror when immersed in water ?

Define focal length of a lens

A double convex lens has 10 cm and 15 cm as its two radii of curvature.The image of an object,placed 30 cm from the lens,is formed at 20 cm from the lens on the other side.Find the refractive index of the material of the lens.Whgat will be the focal length ?What will be the focal length of the lens,if it is immersed in water of refractive index 1.33?

What changes in the focal length of a convex lens occur,when the incident violet light on them is replaced by red light?

Briefly explain,how the focal length of a convex lens changes with increase in wavelength of incident light.

A convex lens of refrative index 1.5 is immersed in a liquid of refractive index: 1.5. what changes happen to the focal length of the lens in the three cases?