Electromagnetic Waves and Spectrum

Cosmic Microwave Background (CMB) radiation is the thermal radiation left over from the Big Bang. It was emitted approximately 380,000 years after the universe began when it had cooled enough for atoms to form. Originally visible light, it has been red-shifted by the expansion of the universe over 13.8 billion years into microwave wavelengths (a few centimeters). This 'afterglow' provides crucial evidence for the Big Bang theory.

Gamma rays have the highest frequency in the electromagnetic spectrum, ranging from 10^19 Hz and above. They are produced by radioactive decay, nuclear explosions, and cosmic events. The electromagnetic spectrum in order of increasing frequency is: radio waves, microwaves, infrared, visible light, UV, X-rays, and gamma rays.

All electromagnetic waves (X-rays, gamma rays, infrared, ultraviolet, and visible light) travel at the same speed in a vacuum - the speed of light (c ≈ 3×10^8 m/s). They are not all affected by magnetic fields, not all damaging to health, and they have very different wavelengths.

The speed of light in vacuum is approximately 3 x 10^8 m/s, commonly rounded to this value in most educational contexts. While more precise values exist (299,792,458 m/s), option C is the accepted standard approximation for the speed of light.

A light year is a unit of distance equal to the distance light travels in one year in a vacuum (approximately 9.46 trillion kilometers or 5.88 trillion miles). It is used to measure vast astronomical distances between stars and galaxies, not time, speed, or energy.

Electromagnetic radiation characterized by wavelength is called light (option C). Light is the visible portion of the electromagnetic spectrum. Sound is a mechanical wave requiring a medium, waves is too general, and kinetics refers to motion studies.

Infrared light has longer wavelengths than visible light, which is why it's invisible to the human eye. The electromagnetic spectrum places infrared just beyond visible red light, with wavelengths extending from about 700 nanometers to 1 millimeter.

A light year is a unit of distance, specifically the distance that light travels in one vacuum year in vacuum. It measures approximately 9.46 trillion kilometers. It is not a measure of energy, speed, or intensity - it's purely a distance measurement used in astronomy.

The energy of a single photon is given by E = hv, where h is Planck's constant and v is the frequency of the electromagnetic radiation. This is a fundamental equation in quantum physics, first proposed by Einstein to explain the photoelectric effect.

Electromagnetic waves are transverse waves that don't require a medium and travel at the speed of light. Infrared, ultraviolet, and X-rays are all parts of the electromagnetic spectrum. Sound waves are mechanical longitudinal waves that require a material medium (solid, liquid, or gas) to propagate and cannot travel through vacuum, making them fundamentally different from electromagnetic waves.

Electromagnetic radiation consists of two major oscillating fields: an electric field and a magnetic field. These fields are perpendicular to each other and to the direction of the wave's propagation.

Wien's displacement law states that hotter objects emit peak radiation at shorter wavelengths. As temperature increases, objects emit more high-frequency (short wavelength) energy including visible light, which is why very hot objects glow from red to white.