Chapter 24, Problem 63PP

Refraction of liquids. The focal length of a mirror can be determined entirely from the shape of the mirror. In contrast, to determine the focal length of a lens, we must know both the shape of the lens and its index of refraction—as well as the index of refraction of the surrounding medium. For instance, when a thin lens is immersed in a liquid, we must modify the thin-lens equation to take into account the refractive properties of the surrounding liquid:

$\frac{1}{f}=\left(\frac{n}{n_{\text{liq}}}-1\right)\left(\frac{1}{R_1}-\frac{2}{R_2}\right)$

where n_liq is the index of refraction of the liquid and n is the index of refraction of the glass.

63. If you place a concave glass lens into a tank of a liquid that has an index of refraction that is greater than that of the lens, what will happen?

1. A.    The lens will no longer be able to create any images.
2. B.     The focal length of the lens will become longer.
3. C.     The focal length of the lens will become shorter.
4. D.    The lens will become a converging lens.