When observing an electromagnetic wave, it is important to understand that the concept of "zero value" refers to the instantaneous values of the electric and magnetic fields at a specific point in space. This point is commonly referred to as the "null point" or "zero crossing." However, it does not mean that the fields cease to exist or that they regenerate themselves at that point.
In reality, an electromagnetic wave is a continuous oscillation of electric and magnetic fields propagating through space. As the wave propagates, the electric and magnetic fields undergo cyclic changes in magnitude and direction. At the null point, both fields momentarily have zero magnitude, but they quickly start to increase in the opposite direction.
The regeneration or continuation of the fields after the null point is a result of the wave's propagation characteristics. An electromagnetic wave consists of oscillating electric and magnetic fields that are perpendicular to each other and perpendicular to the direction of wave propagation. These fields continuously exchange energy as the wave moves through space.
As the wave progresses, the changing magnetic field induces an electric field, and the changing electric field induces a magnetic field. This mutual induction allows the wave to sustain itself and propagate forward. The fields do not need to regenerate; they simply transition from zero magnitude to increasing magnitude and then back to zero again, forming a continuous wave.
To summarize, the zero crossings or null points in an electromagnetic wave represent moments in which the electric and magnetic fields momentarily have zero magnitude. However, the fields regenerate themselves through the continuous exchange of energy as the wave propagates through space, maintaining the wave's oscillatory nature.