ch27_gmjb

Chapter 27 = Light = **27.1 Early Concepts of Light** In the time of the Greek philosophers, light was perceived in many different ways. Some believed that light consisted of tiny particles which entered the eye; others thought that light traveled from the eye to the object that is looked at. However a man named Empedocles believed that all light traveled in waves. In 1905 Albert Einstein discovered that light is made up of photons, though they are particles, the take the characteristics of waves.
 * Photons – ** massless bundles of concentrated electromagnetic energy.

Originally light was said to immediately travel from one place to another. It wasn’t until the late 17th century that light was found to have a finite speed. Ex: it takes about 8 minutes to travel from the Sun to Earth. Speed of Light = Extra Distance Traveled ** / ** Extra Time Measured = 300,000,000km ** / ** 1000s =300,000km/s
 * 27.2 The Speed of Light**
 * Light-year - ** the distance light travels in one year.

When light travels through a transparent material, it is absorbed and re-emitted by the atoms that it strikes. **27.5 Opaque Materials** 27.6 Shadows 27.7 Polarization 27.8 Polarized Light and 3-D Viewing
 * 27.3 Electromagnetic Waves**
 * Electromagnetic wave ** – a wave that is partially magnetic and partially electric
 * Electromagnetic spectrum ** – includes radio waves, microwaves, and x-rays
 * Infrared ** – electromagnetic waves of frequencies lower than visible light
 * Ultraviolet ** – electromagnetic waves of frequencies higher than visible light
 * 27.4 Light and Transparent Materials**
 * Transparent ** – materials that allow light to pass through in straight lines
 * Opaque** – materials that absorb light without reemission and thus allow no light through
 * Ray ** – Thin beam of light
 * Shadow ** – formed where light rays cannot reach
 * Umbra ** – a total shadow
 * Penumbra ** – a partial shadow
 * Polarization ** – the aligning vibrations in a transverse wave, usually by filtering out waves of others directions