Definition
Light (specifically visible light) is the narrow band of electromagnetic radiation that can be detected by the human eye.
Why It Matters
It is the primary sensory channel through which humans gather information about the physical universe.
Core Concepts
- The Spectrum: Includes Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, and Gamma rays.
- Speed of Light (): A constant in a vacuum.
- How to read: “The speed c equals three hundred thousand kilometers per second.”
- Meaning: Universal speed limit for massless particles and EM waves in vacuum—all frequencies share this propagation speed.
- Interaction with Matter:
- Transparent: Light passes through via absorption and reemission (e.g., glass).
- Opaque: Light is absorbed and converted to internal energy (e.g., wood).
- Dual Nature: Light behaves as both a wave (interference, diffraction) and a particle (photoelectric effect/photons).