Final answer:
Electromagnetic radiation is energy, visible as light within the 400-700 nm wavelength range. It travels at about 3.00 × 108 m/s in air, and manifests as both waves and particles, with photons being its quantifiable energy units.
Step-by-step explanation:
Electromagnetic radiation is a form of energy that is often associated with a wavelength that is visible to the human eye. It exists in different wavelengths, each having its own characteristic energy. The portion of electromagnetic radiation that we can see is known as visible light, which has wavelengths roughly between 400-700 nanometers (nm). The entire range of these wavelengths is referred to as the electromagnetic spectrum. Visible light occupies only a very small part of this spectrum, which also includes other types like gamma rays, x-rays, ultraviolet light, infrared light, microwaves, and radio waves.
Notably, all electromagnetic radiation, including visible light, travels through a vacuum at a constant speed, roughly 3.00 × 108 meters per second (m/s), which we conventionally round off to 3.00 × 108 m/s as the speed of light in air. When discussing electromagnetic radiation in terms of particles, we talk about photons, which are packets of energy each having a characteristic wavelength, or what we might perceive as color. The notion of wave-particle duality comes into play here, highlighting that at the quantum level, electromagnetic radiation exhibits both wave-like and particle-like properties.