A spectrum is a condition that is not limited to a specific set of values, but can vary infinitely within a continuum. The word was first used scientifically in optics to describe the rainbow of colors that are visible when white light is dispersed by a prism. However, the term has been expanded to include all types of electromagnetic radiation, from radio waves to gamma rays.
The word “spectrum” is derived from the Latin word for “image” or “appearance”. In physics, a spectrum refers to the distribution of energy as a function of wavelength or frequency. For example, when sunlight passes through a prism, it is separated into its component colors: red, orange, yellow, green, blue and violet. This separation of light into its different wavelengths is called dispersion. A similar effect occurs when sound waves are passed through a medium with different densities; high-density materials cause high pitches and low-density materials cause low pitches.
In many cases, the term “spectrum” is used to refer specifically to the electromagnetic spectrum. The electromagnetic spectrum includes all forms of EM radiation, from radio waves at one end (with long wavelengths) to gamma rays at the other end (with short wavelengths). In between these extremes are microwaves, infrared radiation (IR), visible light and ultraviolet radiation (UV). X-rays lie just outside the visible range; they have shorter wavelengths than UV light but longer wavelengths than gamma rays.
All these different types of EM radiation travel through vacuum at the speed of light; however their speeds can be affected by matter through which they pass. For example, IR Radiation traveling through glass will be slowed down slightly compared to if it were in vacuum because glass is less transparent to IR than it is tovisible light. The amount by which EM Radiation slows down when passing through matter varies according its wavelength – Gamma Rays are hardly affected by any material known while microwaves can be strongly absorbed by water molecules making them very useful for cooking!