Question

what is the difference between ray optics and wave optics?

Answer 1

The ray optics uses the geometry of straight lines to account for the macroscopic pheneomenon like rectilinear propagation of light, reflection and refraction of light etc. However, the microscopic phenomenon like interference, diffraction and polarisation could not be accounted for by ray optics.
To explain these phenomena, concept of waves was introduced. The new branch of physics based on the wave concept of light was called Wave Optics or Physical Optics.