Question

What is the difference between a ray and a wavefront ?

Hint:

Think of a wavefront exactly like the sweeping circular ripple expanding across a pond when a stone is dropped. The rays are just the straight arrows pointing outward from the center, showing you which way the ripple is moving.

Answer 1

Concept:
• Wave optics provides two entirely complementary ways to visualize the propagation of light: discrete rays and continuous wavefronts.
• A wavefront focuses strictly on the phase characteristics of the physical wave.
• A ray focuses strictly on the geometric path and direction of energy transport.

Step 1: Provide a detailed definition of a Wavefront
A completely uniform source of light strictly emits waves in all available directions.
A wavefront is defined geometrically as the continuous locus (or surface) connecting all neighboring points in a medium that are being vibrated in the exact same physical phase at any given instant of time.
For example, if you connect all the precise wave crests expanding outward from a point source, that spherical surface constitutes a spherical wavefront. It represents the actual physical wave structure moving through space.

Step 2: Provide a detailed definition of a Ray
A ray of light is a purely idealized, imaginary line drawn with an arrow that points rigorously in the exact direction of the propagation of the wave's energy.
By fundamental geometric necessity in an isotropic medium, a ray is always strictly drawn perpendicular (normal) to the expanding wavefront surface.
While a wavefront depicts a sweeping surface of identical timing, the ray provides a simple linear vector representing where that surface is heading.