Which statement best describes what happens when light travels from air into water at an angle?

Which statement best describes what happens when light travels from air into water at an angle?

• A. It moves along straight lines in air and continues along the same lines when it enters water.
• B. It moves in a curve in air and moves in straight lines when it enters water.
• C. It moves along straight lines in air and changes direction when it enters water.
• D. It moves in a curve in air and continues moving in the same curve when it enters water.

Answer: (C)

Light travels in straight lines through a uniform medium, but when it meets a boundary between two media with different optical densities, its speed changes and the path bends—that’s refraction. Air has a lower refractive index than water, so entering water from air slows the light and makes it bend toward the normal. If it were moving straight into water (perpendicular to the boundary), there would be no bend, but at an angle it changes direction. So the situation described is straight-line motion in air followed by a change in direction once it crosses into water.

Light travels in straight lines through a uniform medium, but when it meets a boundary between two media with different optical densities, its speed changes and the path bends—that’s refraction. Air has a lower refractive index than water, so entering water from air slows the light and makes it bend toward the normal. If it were moving straight into water (perpendicular to the boundary), there would be no bend, but at an angle it changes direction. So the situation described is straight-line motion in air followed by a change in direction once it crosses into water.