Working of liquid lens we were recently introduced to the liquid lens in school, but i havent quite understood the working of it. I realize that the curvature of the lens is changed by some process, but i dont exactly know what, and how it would work. Itd also be great if you could mention what factors would affect the focal length/ working of a liquid lens.
 A: Considering the physical principles behind it, a liquid lens is no different from a solid one. The focal length $f$ is affected by the refractive index $n$ of the lens material (assuming a refractive index of 1 in the surrounding medium) and the curvatures $R_1$ and $R_2$ of the two surfaces of the lens, as well as it's thickness $d$. It holds
$$
\frac 1f = (n-1) \left( \frac{1}{R_1} - \frac{1}{R_2} + \frac{(n-1)d}{nR_1R_2} \right),
$$
which can also be found at wikipedia and is known as the lensmaker's equation.
For liquid lenses, it is possible to vary the focal distance by changing at least one of the radii and possibly also the thickness. This can be achieved in multiple ways:

*

*This site describes a mechanism that pushes a water droplet on a surface together to decrease the corresponding radius of curvature and increase the thickness at constant lens volume.

*Here liquid is pushed into a cavity formed by a membrane, again increasing thickness and curvature, but at increasing volume.

*On the page referenced by the last link, another technique is described which uses electrical attraction to move the border between two liquids, again changing the curvature.

