In physics, what term describes the phenomenon where a wave changes direction as it passes from one medium to another due to a shift in its speed?

The question describes a phenomenon where a wave changes direction as it moves from one medium to another, and this change in direction is caused by a shift in its speed.

• A. Refraction: This is the bending of a wave as it passes from one medium to another, which occurs because the wave's speed changes in the new medium. This definition perfectly matches the description in the question.
• B. Dispersion: This refers to the separation of a wave into its component frequencies (e.g., white light into a spectrum) due to the dependence of the wave's speed on its frequency in a given medium. While it involves speed changes, it's not the primary term for the general change in direction between media.
• C. Reflection: This is the phenomenon where a wave bounces off a surface and returns into the same medium. It does not involve passing into a new medium.
• D. Diffraction: This is the bending of waves around obstacles or through an opening. It does not primarily involve passing from one medium to another due to a change in speed.

Based on the definitions, Refraction is the term that describes a wave changing direction as it passes from one medium to another due to a shift in its speed.

The correct answer is A.
$\boxed{\text{A. Refraction}}$