How many more minutes would it take light from the Sun to reach Earth if the space between then were filled with water rather than vacuum? [The sun is 1.5 x 10⁸km from Earth.]

$\mu=\frac{C_{o}}{C_{w}} \Rightarrow \frac{4}{3}=\frac{3 \times 10^{8}}{C_{w}} \Rightarrow C_{w}=\frac{3}{4} \times 3 \times 10^{8}=2.25 \times 10^{8} \mathrm{~ms}^{-1}$ $\therefore \mathrm{t}_{1}=\frac{\mathrm{d}}{\mathrm{C}_{\mathrm{w}}}=\frac{1.5 \times 10^{8} \times 10^{3}}{2.25 \times 10^{8} \times 60}=11.11$ minutes $=\frac{100}{9}$ minutes

$\therefore \mathrm{t}_{2}=\frac{\mathrm{d}}{\mathrm{c}_{\mathrm{o}}}=\frac{25}{3}$ minutes $\therefore \Delta \mathrm{t}=\mathrm{t}_{1}-\mathrm{t}_{2}=2.78$ minutes