Wave optics treats light as a wave (electromagnetic wave) and explains phenomena that ray optics cannot: interference, diffraction, and polarization.

Key phenomena explained by wave optics:

• Interference — superposition of two or more coherent waves producing bright and dark fringes (YDSE)
• Diffraction — bending of light around obstacles or through narrow apertures (single slit)
• Polarization — restriction of the electric field oscillation to a single plane (Brewster's law, Malus's law)

Why ray optics fails: Ray optics treats light as straight-line rays and cannot explain why light bends around corners or why thin films show colors. Wave optics is needed whenever the dimensions of apertures or obstacles are comparable to the wavelength of light ($\sim 400$–$700\,\text{nm}$).

NEET Focus: YDSE fringe width formula and variations, three-polaroid problem, Brewster's angle calculation.