# Conceptual Physics Notes on Chapter 27 Light Light

• Slides: 13

Conceptual Physics Notes on Chapter 27 Light

Light Early Concepts of Light Up until the time of Newton, most scientists thought that light was a particle. Dutch scientist Christian Huygens said light was a wave. Then in 1905, Einstein said light was small particles - massless bundles of energy that behaved like waves called photons.

Light Speed of Light In 1675, a Danish astronomer named Olaus Roemer demonstrated that light travels as a finite speed Roemer’s Experiment pg. 405 n Dutch scientist Huygens looked at Roemer’s data and calculated the speed of light to be 300, 000 km/s.

Light n In 1880, an American scientist named Albert Michelson performed a experiment using a spinning mirror to find the speed of light. Michelson’s Experiment

Light

Light n Michelson speed for light (the excepted value today) is 299, 920 km/s. NOTE: We will use Roemer’s rounded number of 300, 000 km/s.

Light FUN FACTS n Light would travel 7. 5 times around Earth in one second. n Light takes 8 minutes to travel from the Sun to Earth - a distance of 93, 000 miles. n Traveling at the speed of light, it would take 4 yrs to travel to the nearest star.

Light Electromagnetic Waves n Electromagnetic Spectrum is a continuous range of waves extending from the longest (Radio) and going to the shortest (Gamma).

Light n Any material that allows light to pass through in straight lines is said to be transparent. n EX: Glass Water n Any material that absorbs light w/o reemission is said to be opaque. n EX: Wood Stone

Light SHADOWS n A thin beam of light is called a Ray. When light rays can not go past an object, a shadow is formed. Two parts of a shadow are: n umbra: a total shadow. n penumbra: a partial shadow. n EX: Solar and Lunar Eclipses n See pg. 413 Fig. 27. 12 & 27. 13

Light POLARIZATION n Light is a transverse wave. White light is Non-polarized. n When passed through a filter (Polarizer) only light that is moving same as the filter opening will make it through. – See pg. 415 Fig. 27. 18

Light