A converging lens made of glass (n=1.5) is placed under...

A converging lens made of glass $(n=1.5)$ is placed under water $(n=1.33)$. Describe how the focal length of the lens under water compares to the focal length in air? Draw a diagram to illustrate your answer.

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Key Concepts

Lensmaker's Equation

The lensmaker's equation relates the focal length of a lens to its radii of curvature and the refractive indices of the lens material and the surrounding medium. It is crucial in understanding how changes in the surrounding medium affect the focal length since the optical power of the lens depends on the relative difference between the refractive index of the lens and that of the medium.

Refractive Index Contrast

The concept of refractive index contrast describes the difference in optical density between two materials—in this case, the lens material and its environment. When a lens is immersed in a medium with a refractive index closer to that of the lens, the contrast decreases, which in turn reduces the lens's optical power and increases its focal length.

Effect of Surrounding Medium on Focal Length

The surrounding medium significantly influences the effective focal length of a lens. A lens designed for use in air will behave differently when placed in water due to a change in the surrounding refractive index. As the surrounding medium’s refractive index increases, the focal length becomes longer because the relative bending of light rays at the lens surfaces is reduced.

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