Notes on Light and Matter

Light as Energy: Light is experienced as radiant energy; it interacts with matter in various ways, affecting our perception of heat and light.
Measurement of Energy: Power (rate of energy transfer) is measured in watts. 1 watt = 1 joule/second. Humans have an average power requirement of about 10 million joules/day.
Color Perception:
- Light is perceived in colors, which represent different wavelengths. White light combines all colors; black indicates no light.
- Different colors arise from mixtures of primary colors (red, green, blue).

Nature of Light: Light is both a wave (electromagnetic wave) and a particle (photon) with properties such as wavelength and frequency.
Electromagnetic Spectrum: The spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Structure of Matter:
- Composed of atoms (which include protons, neutrons, and electrons).
- Different chemical elements have unique atomic structures (e.g., hydrogen has 1 proton; carbon has 6).
Phases of Matter: Matter exists as solids, liquids, and gases; phases can change due to temperature and pressure.
- Changes: Solid (ice) → Liquid (water) → Gas (water vapor); at high temperatures, dissociation occurs.

Spectra Types: Three basic types of spectra:
1. Continuous Spectrum: A smooth rainbow of colors produced by incandescent sources (e.g., light bulbs).
2. Emission Line Spectrum: Bright lines on a dark background indicating specific wavelengths emitted by hot gases.
3. Absorption Line Spectrum: Dark lines on a continuous spectrum where certain wavelengths have been absorbed, indicating the presence of specific elements.
Chemical Composition: Emission and absorption lines are unique to each element, providing fingerprints for identification in celestial bodies.
Temperature Determination: Thermal radiation spectra allow us to estimate the temperature of stars and other objects based on their color and intensity.

Wien's Law: Hotter objects emit higher energy and shorter wavelength radiation.
Stefan-Boltzmann Law: Hotter objects emit more total light per unit surface area.

The Doppler effect describes changes in the wavelength of light due to the motion of the source relative to the observer:
- Blueshift: Light from an object moving toward us, indicating shorter wavelengths.
- Redshift: Light from a receding object, indicating longer wavelengths.
Motion Dynamics: Spectral lines help determine the radial velocity of celestial objects. The broader lines indicate rotation rates.