The bending of light when it passes from air into water is an example of which phenomenon?

• A. Reflection
• B. Absorption
• C. Diffraction
• D. Refraction

Answer: (D)

This question tests refraction, the bending of light when it passes from one medium into another because its speed changes. When light moves from air into water, it slows down. Because the speed changes at the boundary, the light ray changes direction as it enters the water, bending toward the line perpendicular to the surface (the normal). This effect is described by Snell’s law, which shows how the angles relate to the refractive indices of air and water; since water is denser than air, the refracted ray makes a smaller angle with the normal than the incoming ray does.

A common everyday example is a straw in a glass of water looking bent at the surface, illustrating refraction.

It isn’t reflection, which would be light bouncing back into the air, and it isn’t absorption, which is light energy being taken up by the medium, nor diffraction, which involves bending around edges or through narrow openings.