The velocity of light in a medium can be calculated using the formula:
v = c / n
where v is the velocity of light in the medium, c is the velocity of light in vacuum (approximately 3 x 10^8 m/s), and n is the refractive index of the medium.
In this case, if the refractive index of water is nw = 1.3, we can calculate the velocity of light in water as follows:
v_water = c / nw
v_water = (3 x 10^8 m/s) / 1.3
v_water ≈ 2.31 x 10^8 m/s
Therefore, the velocity of light in water is approximately 2.31 x 10^8 m/s.