Why can a ray be used to represent light in a ray diagram? A. Light waves are electromagnetic waves.
B. Light waves spread out in all directions.
C. Light waves travel in straight lines.
D. Light waves can be reflected or refracted.

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.