Chapter 34 - Geometric Optics - Problems - Exercises - Page 1152: 34.20

5.32 m.

For a plane refracting surface, $\frac{n_a}{s}+\frac{n_b}{s’}=0$. We know that $n_a=1.33$ and we are looking for s. We see that $n_b = 1.00$. The image is 4.00m below the surface of the water, so s’=-4.00 m. $$\frac{n_a}{s}+\frac{n_b}{s’}=0$$ $$\frac{1.33}{s}+\frac{1.00}{-4.00m}=0$$ $$s=(4.00m)\frac{1.33}{1.00}=5.32m$$