Light travels through a closed cylindrical tube filled with a gas. As the gas is gradually pumped out, the speed of light inside the tube will

Step-by-step solution

The speed of light in a medium is given by v = c , where c is the speed of light in vacuum and is the refractive index of the medium. The refractive index of a gas is slightly greater than 1 . As the gas is gradually pumped out, the density of the gas decreases, causing the medium inside the tube to approach a vacuum. Consequently, the refractive index of the gas decreases towards 1 . Since the refractive index decreases, the speed of light v inside the tube increases.