A light wave is described by the equation y = A (kx - ω t) . In...

Light is an electromagnetic wave consisting of oscillating electric and magnetic fields that propagate through space.

The given equation $y = A \sin(kx - \omega t)$ represents the propagation of a light wave, where $y$ denotes the instantaneous value of the oscillating electric field (or magnetic field).

Pressure and density variations are characteristics of longitudinal mechanical waves, such as sound waves.

The concept of ether particles is obsolete as electromagnetic waves do not require a material medium for propagation.

Therefore, $y$ represents the electric field.